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 $56.29   3.640%   $58.339   $58.34   $58.35   $58.30  
  Purchase #2 $227.35   9.389%   $248.6959   $248.70   $248.70   $248.70  
  Purchase #3 $60.54   8.513%   $65.6938   $65.69   $65.70   $65.70  
  Purchase #4 $60.52   7.331%   $64.9567   $64.96   $64.95   $65.00  
  Purchase #5 $41.32   7.847%   $44.5624   $44.56   $44.55   $44.60  
  Purchase #6 $84.64   13.143%   $95.7642   $95.76   $95.75   $95.80  
  Purchase #7 $194.82   13.245%   $220.6239   $220.62   $220.60   $220.60  
  7 purchase totals = $725.48       $798.6359   $798.63   $798.60   $798.70