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 $76.33   13.675%   $86.7681   $86.77   $86.75   $86.80  
  Purchase #2 $153.62   3.475%   $158.9583   $158.96   $158.95   $159.00  
  Purchase #3 $67.46   5.258%   $71.007   $71.01   $71.00   $71.00  
  Purchase #4 $151.39   4.340%   $157.9603   $157.96   $157.95   $158.00  
  Purchase #5 $40.31   10.373%   $44.4914   $44.49   $44.50   $44.50  
  Purchase #6 $185.62   4.822%   $194.5706   $194.57   $194.55   $194.60  
  Purchase #7 $22.87   12.772%   $25.791   $25.79   $25.80   $25.80  
  7 purchase totals = $697.60       $739.5467   $739.55   $739.50   $739.70