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 $224.98   3.620%   $233.1243   $233.12   $233.10   $233.10  
  Purchase #2 $113.97   13.133%   $128.9377   $128.94   $128.95   $128.90  
  Purchase #3 $74.85   4.624%   $78.3111   $78.31   $78.30   $78.30  
  Purchase #4 $67.37   11.812%   $75.3277   $75.33   $75.35   $75.30  
  Purchase #5 $242.63   8.283%   $262.727   $262.73   $262.75   $262.70  
  Purchase #6 $187.69   7.670%   $202.0858   $202.09   $202.10   $202.10  
  Purchase #7 $46.67   12.847%   $52.6657   $52.67   $52.65   $52.70  
  7 purchase totals = $958.16       $1,033.1793   $1,033.19   $1,033.20   $1,033.10