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 $29.81   9.764%   $32.7206   $32.72   $32.70   $32.70  
  Purchase #2 $104.86   10.270%   $115.6291   $115.63   $115.65   $115.60  
  Purchase #3 $78.36   6.484%   $83.4409   $83.44   $83.45   $83.40  
  Purchase #4 $194.96   7.300%   $209.1921   $209.19   $209.20   $209.20  
  Purchase #5 $60.96   13.149%   $68.9756   $68.98   $69.00   $69.00  
  Purchase #6 $126.64   8.417%   $137.2993   $137.30   $137.30   $137.30  
  Purchase #7 $95.51   6.344%   $101.5692   $101.57   $101.55   $101.60  
  7 purchase totals = $691.10       $748.8268   $748.83   $748.85   $748.80