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 $162.43   6.681%   $173.2819   $173.28   $173.30   $173.30  
  Purchase #2 $77.89   12.569%   $87.68   $87.68   $87.70   $87.70  
  Purchase #3 $95.75   6.201%   $101.6875   $101.69   $101.70   $101.70  
  Purchase #4 $82.34   3.521%   $85.2392   $85.24   $85.25   $85.20  
  Purchase #5 $141.32   6.109%   $149.9532   $149.95   $149.95   $150.00  
  Purchase #6 $80.58   5.733%   $85.1997   $85.20   $85.20   $85.20  
  Purchase #7 $43.85   7.704%   $47.2282   $47.23   $47.25   $47.20  
  7 purchase totals = $684.16       $730.2697   $730.27   $730.35   $730.30