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 $154.67   3.824%   $160.5846   $160.58   $160.60   $160.60  
  Purchase #2 $7.63   7.574%   $8.2079   $8.21   $8.20   $8.20  
  Purchase #3 $164.58   3.601%   $170.5065   $170.51   $170.50   $170.50  
  Purchase #4 $123.27   9.801%   $135.3517   $135.35   $135.35   $135.40  
  Purchase #5 $202.86   8.845%   $220.803   $220.80   $220.80   $220.80  
  Purchase #6 $234.85   10.803%   $260.2208   $260.22   $260.20   $260.20  
  Purchase #7 $152.97   3.407%   $158.1817   $158.18   $158.20   $158.20  
  7 purchase totals = $1,040.83       $1,113.8562   $1,113.85   $1,113.85   $1,113.90