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 $91.73   6.267%   $97.4787   $97.48   $97.50   $97.50  
  Purchase #2 $222.31   6.360%   $236.4489   $236.45   $236.45   $236.40  
  Purchase #3 $115.88   8.558%   $125.797   $125.80   $125.80   $125.80  
  Purchase #4 $237.68   4.437%   $248.2259   $248.23   $248.25   $248.20  
  Purchase #5 $179.48   9.560%   $196.6383   $196.64   $196.65   $196.60  
  Purchase #6 $95.38   11.393%   $106.2466   $106.25   $106.25   $106.20  
  Purchase #7 $241.46   9.523%   $264.4542   $264.45   $264.45   $264.50  
  7 purchase totals = $1,183.92       $1,275.2896   $1,275.30   $1,275.35   $1,275.20