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 $118.59   7.175%   $127.0988   $127.10   $127.10   $127.10  
  Purchase #2 $56.96   12.694%   $64.1905   $64.19   $64.20   $64.20  
  Purchase #3 $224.49   13.490%   $254.7737   $254.77   $254.75   $254.80  
  Purchase #4 $79.68   6.554%   $84.9022   $84.90   $84.90   $84.90  
  Purchase #5 $113.98   3.686%   $118.1813   $118.18   $118.20   $118.20  
  Purchase #6 $151.64   11.844%   $169.6002   $169.60   $169.60   $169.60  
  Purchase #7 $194.53   4.201%   $202.7022   $202.70   $202.70   $202.70  
  7 purchase totals = $939.87       $1,021.4489   $1,021.44   $1,021.45   $1,021.50