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 $55.95   8.267%   $60.5754   $60.58   $60.60   $60.60  
  Purchase #2 $231.96   10.422%   $256.1349   $256.13   $256.15   $256.10  
  Purchase #3 $146.83   6.410%   $156.2418   $156.24   $156.25   $156.20  
  Purchase #4 $234.58   13.647%   $266.5931   $266.59   $266.60   $266.60  
  Purchase #5 $195.93   4.781%   $205.2974   $205.30   $205.30   $205.30  
  Purchase #6 $114.58   6.263%   $121.7561   $121.76   $121.75   $121.80  
  Purchase #7 $155.36   3.211%   $160.3486   $160.35   $160.35   $160.30  
  7 purchase totals = $1,135.19       $1,226.9473   $1,226.95   $1,227.00   $1,226.90