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 $46.73   3.839%   $48.524   $48.52   $48.50   $48.50  
  Purchase #2 $230.55   5.113%   $242.338   $242.34   $242.35   $242.30  
  Purchase #3 $236.72   6.248%   $251.5103   $251.51   $251.50   $251.50  
  Purchase #4 $240.73   3.751%   $249.7598   $249.76   $249.75   $249.80  
  Purchase #5 $120.43   12.414%   $135.3802   $135.38   $135.40   $135.40  
  Purchase #6 $235.38   5.660%   $248.7025   $248.70   $248.70   $248.70  
  Purchase #7 $214.43   13.527%   $243.4359   $243.44   $243.45   $243.40  
  7 purchase totals = $1,324.97       $1,419.6507   $1,419.65   $1,419.65   $1,419.60