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 $55.30   7.742%   $59.5813   $59.58   $59.60   $59.60  
  Purchase #2 $208.42   7.475%   $223.9994   $224.00   $224.00   $224.00  
  Purchase #3 $227.45   6.109%   $241.3449   $241.34   $241.35   $241.30  
  Purchase #4 $124.34   7.765%   $133.995   $134.00   $134.00   $134.00  
  Purchase #5 $133.63   11.252%   $148.666   $148.67   $148.65   $148.70  
  Purchase #6 $29.46   6.408%   $31.3478   $31.35   $31.35   $31.30  
  Purchase #7 $80.51   10.443%   $88.9177   $88.92   $88.90   $88.90  
  7 purchase totals = $859.11       $927.8521   $927.86   $927.85   $927.80