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 $120.93   3.445%   $125.096   $125.10   $125.10   $125.10  
  Purchase #2 $92.66   5.676%   $97.9194   $97.92   $97.90   $97.90  
  Purchase #3 $41.69   6.472%   $44.3882   $44.39   $44.40   $44.40  
  Purchase #4 $190.44   4.119%   $198.2842   $198.28   $198.30   $198.30  
  Purchase #5 $245.57   12.776%   $276.944   $276.94   $276.95   $276.90  
  Purchase #6 $241.42   7.767%   $260.1711   $260.17   $260.15   $260.20  
  Purchase #7 $161.85   5.238%   $170.3277   $170.33   $170.35   $170.30  
  7 purchase totals = $1,094.56       $1,173.1306   $1,173.13   $1,173.15   $1,173.10