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 $59.95   7.331%   $64.3449   $64.34   $64.35   $64.30  
  Purchase #2 $38.65   7.214%   $41.4382   $41.44   $41.45   $41.40  
  Purchase #3 $248.68   7.296%   $266.8237   $266.82   $266.80   $266.80  
  Purchase #4 $90.46   5.392%   $95.3376   $95.34   $95.35   $95.30  
  Purchase #5 $162.51   10.275%   $179.2079   $179.21   $179.20   $179.20  
  Purchase #6 $108.32   6.574%   $115.441   $115.44   $115.45   $115.40  
  Purchase #7 $200.90   10.791%   $222.5791   $222.58   $222.60   $222.60  
  7 purchase totals = $909.47       $985.1724   $985.17   $985.20   $985.00