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 $38.39   13.707%   $43.6521   $43.65   $43.65   $43.70  
  Purchase #2 $59.41   10.516%   $65.6576   $65.66   $65.65   $65.70  
  Purchase #3 $31.73   11.797%   $35.4732   $35.47   $35.45   $35.50  
  Purchase #4 $212.40   9.511%   $232.6014   $232.60   $232.60   $232.60  
  Purchase #5 $175.31   11.211%   $194.964   $194.96   $194.95   $195.00  
  Purchase #6 $171.66   6.639%   $183.0565   $183.06   $183.05   $183.10  
  Purchase #7 $194.48   5.255%   $204.6999   $204.70   $204.70   $204.70  
  7 purchase totals = $883.38       $960.1047   $960.10   $960.05   $960.30