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 $206.97   13.206%   $234.3025   $234.30   $234.30   $234.30  
  Purchase #2 $185.75   7.483%   $199.6497   $199.65   $199.65   $199.60  
  Purchase #3 $245.32   12.500%   $275.985   $275.99   $276.00   $276.00  
  Purchase #4 $77.36   12.132%   $86.7453   $86.75   $86.75   $86.70  
  Purchase #5 $68.92   5.612%   $72.7878   $72.79   $72.80   $72.80  
  Purchase #6 $129.88   13.141%   $146.9475   $146.95   $146.95   $146.90  
  Purchase #7 $7.84   6.765%   $8.3704   $8.37   $8.35   $8.40  
  7 purchase totals = $922.04       $1,024.7882   $1,024.80   $1,024.80   $1,024.70