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 $84.51   4.598%   $88.3958   $88.40   $88.40   $88.40  
  Purchase #2 $152.92   5.764%   $161.7343   $161.73   $161.75   $161.70  
  Purchase #3 $26.32   13.211%   $29.7971   $29.80   $29.80   $29.80  
  Purchase #4 $149.78   8.223%   $162.0964   $162.10   $162.10   $162.10  
  Purchase #5 $129.35   12.702%   $145.78   $145.78   $145.80   $145.80  
  Purchase #6 $36.96   9.651%   $40.527   $40.53   $40.55   $40.50  
  Purchase #7 $116.53   12.186%   $130.7303   $130.73   $130.75   $130.70  
  7 purchase totals = $696.37       $759.0609   $759.07   $759.15   $759.00