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 $73.47   6.232%   $78.0487   $78.05   $78.05   $78.00  
  Purchase #2 $141.92   12.492%   $159.6486   $159.65   $159.65   $159.60  
  Purchase #3 $227.42   5.777%   $240.5581   $240.56   $240.55   $240.60  
  Purchase #4 $247.34   8.464%   $268.2749   $268.27   $268.25   $268.30  
  Purchase #5 $224.96   12.594%   $253.2915   $253.29   $253.30   $253.30  
  Purchase #6 $130.26   4.583%   $136.2298   $136.23   $136.25   $136.20  
  Purchase #7 $62.89   6.121%   $66.7395   $66.74   $66.75   $66.70  
  7 purchase totals = $1,108.26       $1,202.7911   $1,202.79   $1,202.80   $1,202.70