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 $204.76   13.306%   $232.0054   $232.01   $232.00   $232.00  
  Purchase #2 $191.98   12.815%   $216.5822   $216.58   $216.60   $216.60  
  Purchase #3 $201.62   8.232%   $218.2174   $218.22   $218.20   $218.20  
  Purchase #4 $13.65   9.415%   $14.9351   $14.94   $14.95   $14.90  
  Purchase #5 $229.71   10.569%   $253.988   $253.99   $254.00   $254.00  
  Purchase #6 $36.29   11.338%   $40.4046   $40.40   $40.40   $40.40  
  Purchase #7 $89.29   13.744%   $101.562   $101.56   $101.55   $101.60  
  7 purchase totals = $967.30       $1,077.6947   $1,077.70   $1,077.70   $1,077.70