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 $245.46   8.605%   $266.5818   $266.58   $266.60   $266.60  
  Purchase #2 $215.63   11.110%   $239.5865   $239.59   $239.60   $239.60  
  Purchase #3 $117.95   5.432%   $124.357   $124.36   $124.35   $124.40  
  Purchase #4 $92.93   7.862%   $100.2362   $100.24   $100.25   $100.20  
  Purchase #5 $20.93   8.587%   $22.7273   $22.73   $22.75   $22.70  
  Purchase #6 $132.97   12.134%   $149.1046   $149.10   $149.10   $149.10  
  Purchase #7 $202.51   5.568%   $213.7858   $213.79   $213.80   $213.80  
  7 purchase totals = $1,028.38       $1,116.3792   $1,116.39   $1,116.45   $1,116.40