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 $168.67   8.146%   $182.4099   $182.41   $182.40   $182.40  
  Purchase #2 $26.78   6.222%   $28.4463   $28.45   $28.45   $28.40  
  Purchase #3 $143.50   13.257%   $162.5238   $162.52   $162.50   $162.50  
  Purchase #4 $247.73   12.267%   $278.119   $278.12   $278.10   $278.10  
  Purchase #5 $229.26   5.549%   $241.9816   $241.98   $242.00   $242.00  
  Purchase #6 $206.98   9.171%   $225.9621   $225.96   $225.95   $226.00  
  Purchase #7 $45.32   3.740%   $47.015   $47.02   $47.00   $47.00  
  7 purchase totals = $1,068.24       $1,166.4577   $1,166.46   $1,166.40   $1,166.40