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 $186.58   4.566%   $195.0992   $195.10   $195.10   $195.10  
  Purchase #2 $161.77   11.793%   $180.8475   $180.85   $180.85   $180.80  
  Purchase #3 $155.95   8.165%   $168.6833   $168.68   $168.70   $168.70  
  Purchase #4 $67.81   10.530%   $74.9504   $74.95   $74.95   $75.00  
  Purchase #5 $104.66   10.701%   $115.8597   $115.86   $115.85   $115.90  
  Purchase #6 $112.94   3.505%   $116.8985   $116.90   $116.90   $116.90  
  Purchase #7 $168.78   5.574%   $178.1878   $178.19   $178.20   $178.20  
  7 purchase totals = $958.49       $1,030.5264   $1,030.53   $1,030.55   $1,030.60