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 $43.49   12.102%   $48.7532   $48.75   $48.75   $48.80  
  Purchase #2 $32.46   6.476%   $34.5621   $34.56   $34.55   $34.60  
  Purchase #3 $11.69   8.401%   $12.6721   $12.67   $12.65   $12.70  
  Purchase #4 $165.61   7.761%   $178.463   $178.46   $178.45   $178.50  
  Purchase #5 $21.78   3.810%   $22.6098   $22.61   $22.60   $22.60  
  Purchase #6 $86.61   10.823%   $95.9838   $95.98   $96.00   $96.00  
  Purchase #7 $15.97   6.261%   $16.9699   $16.97   $16.95   $17.00  
  7 purchase totals = $377.61       $410.0139   $410.00   $409.95   $410.20