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 $40.53   9.205%   $44.2608   $44.26   $44.25   $44.30  
  Purchase #2 $89.87   8.443%   $97.4577   $97.46   $97.45   $97.50  
  Purchase #3 $223.41   5.623%   $235.9723   $235.97   $235.95   $236.00  
  Purchase #4 $191.92   3.755%   $199.1266   $199.13   $199.15   $199.10  
  Purchase #5 $125.72   6.160%   $133.4644   $133.46   $133.45   $133.50  
  Purchase #6 $208.29   5.260%   $219.2461   $219.25   $219.25   $219.20  
  Purchase #7 $109.73   6.433%   $116.7889   $116.79   $116.80   $116.80  
  7 purchase totals = $989.47       $1,046.3168   $1,046.32   $1,046.30   $1,046.40