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 $169.73   12.825%   $191.4979   $191.50   $191.50   $191.50  
  Purchase #2 $33.57   3.315%   $34.6828   $34.68   $34.70   $34.70  
  Purchase #3 $151.93   9.743%   $166.7325   $166.73   $166.75   $166.70  
  Purchase #4 $102.67   13.706%   $116.742   $116.74   $116.75   $116.70  
  Purchase #5 $239.36   11.677%   $267.3101   $267.31   $267.30   $267.30  
  Purchase #6 $178.76   10.325%   $197.217   $197.22   $197.20   $197.20  
  Purchase #7 $121.94   8.722%   $132.5756   $132.58   $132.60   $132.60  
  7 purchase totals = $997.96       $1,106.7579   $1,106.76   $1,106.80   $1,106.70