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 $239.70   11.775%   $267.9247   $267.92   $267.90   $267.90  
  Purchase #2 $165.35   10.764%   $183.1483   $183.15   $183.15   $183.10  
  Purchase #3 $56.52   12.600%   $63.6415   $63.64   $63.65   $63.60  
  Purchase #4 $154.36   3.143%   $159.2115   $159.21   $159.20   $159.20  
  Purchase #5 $209.90   7.290%   $225.2017   $225.20   $225.20   $225.20  
  Purchase #6 $117.33   8.687%   $127.5225   $127.52   $127.50   $127.50  
  Purchase #7 $59.77   10.606%   $66.1092   $66.11   $66.10   $66.10  
  7 purchase totals = $1,002.93       $1,092.7594   $1,092.75   $1,092.70   $1,092.60