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 $215.94   8.754%   $234.8434   $234.84   $234.85   $234.80  
  Purchase #2 $181.63   12.413%   $204.1757   $204.18   $204.20   $204.20  
  Purchase #3 $235.28   12.390%   $264.4312   $264.43   $264.45   $264.40  
  Purchase #4 $237.65   10.498%   $262.5985   $262.60   $262.60   $262.60  
  Purchase #5 $249.90   11.417%   $278.4311   $278.43   $278.45   $278.40  
  Purchase #6 $76.77   8.111%   $82.9968   $83.00   $83.00   $83.00  
  Purchase #7 $32.45   8.463%   $35.1962   $35.20   $35.20   $35.20  
  7 purchase totals = $1,229.62       $1,362.6729   $1,362.68   $1,362.75   $1,362.60