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 $248.49   7.477%   $267.0696   $267.07   $267.05   $267.10  
  Purchase #2 $219.80   11.142%   $244.2901   $244.29   $244.30   $244.30  
  Purchase #3 $29.45   13.673%   $33.4767   $33.48   $33.50   $33.50  
  Purchase #4 $88.48   9.694%   $97.0573   $97.06   $97.05   $97.10  
  Purchase #5 $177.34   3.139%   $182.9067   $182.91   $182.90   $182.90  
  Purchase #6 $187.67   13.184%   $212.4124   $212.41   $212.40   $212.40  
  Purchase #7 $172.31   9.754%   $189.1171   $189.12   $189.10   $189.10  
  7 purchase totals = $1,123.54       $1,226.3299   $1,226.34   $1,226.30   $1,226.40