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 $233.34   11.449%   $260.0551   $260.06   $260.05   $260.10  
  Purchase #2 $165.57   8.823%   $180.1782   $180.18   $180.20   $180.20  
  Purchase #3 $244.37   5.146%   $256.9453   $256.95   $256.95   $256.90  
  Purchase #4 $151.31   3.588%   $156.739   $156.74   $156.75   $156.70  
  Purchase #5 $71.84   6.433%   $76.4615   $76.46   $76.45   $76.50  
  Purchase #6 $205.54   7.712%   $221.3912   $221.39   $221.40   $221.40  
  Purchase #7 $195.76   11.653%   $218.5719   $218.57   $218.55   $218.60  
  7 purchase totals = $1,267.73       $1,370.3422   $1,370.35   $1,370.35   $1,370.40