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 $246.70   5.497%   $260.2611   $260.26   $260.25   $260.30  
  Purchase #2 $120.34   10.196%   $132.6099   $132.61   $132.60   $132.60  
  Purchase #3 $104.76   13.548%   $118.9529   $118.95   $118.95   $119.00  
  Purchase #4 $184.43   10.610%   $203.998   $204.00   $204.00   $204.00  
  Purchase #5 $114.61   10.310%   $126.4263   $126.43   $126.45   $126.40  
  Purchase #6 $167.93   9.757%   $184.3149   $184.31   $184.30   $184.30  
  Purchase #7 $93.31   3.331%   $96.4182   $96.42   $96.40   $96.40  
  7 purchase totals = $1,032.08       $1,122.9813   $1,122.98   $1,122.95   $1,123.00