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 $84.29   13.638%   $95.7855   $95.79   $95.80   $95.80  
  Purchase #2 $235.99   10.180%   $260.0138   $260.01   $260.00   $260.00  
  Purchase #3 $42.33   8.516%   $45.9348   $45.93   $45.95   $45.90  
  Purchase #4 $16.26   4.510%   $16.9933   $16.99   $17.00   $17.00  
  Purchase #5 $69.41   13.132%   $78.5249   $78.52   $78.50   $78.50  
  Purchase #6 $59.35   6.132%   $62.9893   $62.99   $63.00   $63.00  
  Purchase #7 $74.27   11.228%   $82.609   $82.61   $82.60   $82.60  
  7 purchase totals = $581.90       $642.8506   $642.84   $642.85   $642.80