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 $65.49   12.397%   $73.6088   $73.61   $73.60   $73.60  
  Purchase #2 $226.51   11.130%   $251.7206   $251.72   $251.70   $251.70  
  Purchase #3 $108.79   4.264%   $113.4288   $113.43   $113.45   $113.40  
  Purchase #4 $80.93   12.740%   $91.2405   $91.24   $91.25   $91.20  
  Purchase #5 $241.78   9.738%   $265.3245   $265.32   $265.30   $265.30  
  Purchase #6 $213.39   11.779%   $238.5252   $238.53   $238.55   $238.50  
  Purchase #7 $231.28   8.844%   $251.7344   $251.73   $251.75   $251.70  
  7 purchase totals = $1,168.17       $1,285.5828   $1,285.58   $1,285.60   $1,285.40