Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $216.66   9.673%   $237.6175   $237.62   $237.60   $237.60  
  Purchase #2 $123.39   11.560%   $137.6539   $137.65   $137.65   $137.70  
  Purchase #3 $204.57   10.361%   $225.7655   $225.77   $225.75   $225.80  
  Purchase #4 $150.35   11.104%   $167.0449   $167.04   $167.05   $167.00  
  Purchase #5 $105.90   13.110%   $119.7835   $119.78   $119.80   $119.80  
  Purchase #6 $246.52   4.609%   $257.8821   $257.88   $257.90   $257.90  
  Purchase #7 $226.83   5.866%   $240.1358   $240.14   $240.15   $240.10  
  7 purchase totals = $1,274.22       $1,385.8832   $1,385.88   $1,385.90   $1,385.90