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 $174.86   9.667%   $191.7637   $191.76   $191.75   $191.80  
  Purchase #2 $248.84   10.747%   $275.5828   $275.58   $275.60   $275.60  
  Purchase #3 $235.39   4.306%   $245.5259   $245.53   $245.55   $245.50  
  Purchase #4 $130.47   9.725%   $143.1582   $143.16   $143.15   $143.20  
  Purchase #5 $221.27   6.573%   $235.8141   $235.81   $235.80   $235.80  
  Purchase #6 $119.97   12.692%   $135.1966   $135.20   $135.20   $135.20  
  Purchase #7 $138.47   8.248%   $149.891   $149.89   $149.90   $149.90  
  7 purchase totals = $1,269.27       $1,376.9323   $1,376.93   $1,376.95   $1,377.00