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 $74.46   11.642%   $83.1286   $83.13   $83.15   $83.10  
  Purchase #2 $244.54   12.459%   $275.0072   $275.01   $275.00   $275.00  
  Purchase #3 $45.39   8.471%   $49.235   $49.24   $49.25   $49.20  
  Purchase #4 $138.81   13.561%   $157.634   $157.63   $157.65   $157.60  
  Purchase #5 $14.58   13.870%   $16.6022   $16.60   $16.60   $16.60  
  Purchase #6 $125.52   12.449%   $141.146   $141.15   $141.15   $141.10  
  Purchase #7 $219.70   5.592%   $231.9856   $231.99   $232.00   $232.00  
  7 purchase totals = $863.00       $954.7386   $954.75   $954.80   $954.60