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 $34.72   7.146%   $37.2011   $37.20   $37.20   $37.20  
  Purchase #2 $33.57   3.289%   $34.6741   $34.67   $34.65   $34.70  
  Purchase #3 $141.59   13.366%   $160.5149   $160.51   $160.50   $160.50  
  Purchase #4 $56.57   10.717%   $62.6326   $62.63   $62.65   $62.60  
  Purchase #5 $241.34   11.664%   $269.4899   $269.49   $269.50   $269.50  
  Purchase #6 $81.65   6.716%   $87.1336   $87.13   $87.15   $87.10  
  Purchase #7 $149.53   11.272%   $166.385   $166.39   $166.40   $166.40  
  7 purchase totals = $738.97       $818.0312   $818.02   $818.05   $818.00