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 $50.77   4.713%   $53.1628   $53.16   $53.15   $53.20  
  Purchase #2 $160.73   9.771%   $176.4349   $176.43   $176.45   $176.40  
  Purchase #3 $174.89   10.644%   $193.5053   $193.51   $193.50   $193.50  
  Purchase #4 $96.95   5.433%   $102.2173   $102.22   $102.20   $102.20  
  Purchase #5 $112.41   3.765%   $116.6422   $116.64   $116.65   $116.60  
  Purchase #6 $169.26   5.376%   $178.3594   $178.36   $178.35   $178.40  
  Purchase #7 $218.63   6.201%   $232.1872   $232.19   $232.20   $232.20  
  7 purchase totals = $983.64       $1,052.5091   $1,052.51   $1,052.50   $1,052.50