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 $186.97   6.607%   $199.3231   $199.32   $199.30   $199.30  
  Purchase #2 $155.50   6.123%   $165.0213   $165.02   $165.00   $165.00  
  Purchase #3 $59.78   10.765%   $66.2153   $66.22   $66.20   $66.20  
  Purchase #4 $76.28   12.717%   $85.9805   $85.98   $86.00   $86.00  
  Purchase #5 $16.56   11.365%   $18.442   $18.44   $18.45   $18.40  
  Purchase #6 $229.67   6.831%   $245.3588   $245.36   $245.35   $245.40  
  Purchase #7 $157.27   9.590%   $172.3522   $172.35   $172.35   $172.40  
  7 purchase totals = $882.03       $952.6932   $952.69   $952.65   $952.70