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 $56.95   13.577%   $64.6821   $64.68   $64.70   $64.70  
  Purchase #2 $241.39   5.360%   $254.3285   $254.33   $254.35   $254.30  
  Purchase #3 $45.58   11.728%   $50.9256   $50.93   $50.95   $50.90  
  Purchase #4 $85.26   11.249%   $94.8509   $94.85   $94.85   $94.90  
  Purchase #5 $25.41   7.569%   $27.3333   $27.33   $27.35   $27.30  
  Purchase #6 $237.66   6.393%   $252.8536   $252.85   $252.85   $252.90  
  Purchase #7 $59.30   7.145%   $63.537   $63.54   $63.55   $63.50  
  7 purchase totals = $751.55       $808.5110   $808.51   $808.60   $808.50