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 $169.54   8.595%   $184.112   $184.11   $184.10   $184.10  
  Purchase #2 $103.83   8.290%   $112.4375   $112.44   $112.45   $112.40  
  Purchase #3 $72.31   4.660%   $75.6796   $75.68   $75.70   $75.70  
  Purchase #4 $188.90   3.191%   $194.9278   $194.93   $194.95   $194.90  
  Purchase #5 $244.54   11.222%   $271.9823   $271.98   $272.00   $272.00  
  Purchase #6 $230.83   13.550%   $262.1075   $262.11   $262.10   $262.10  
  Purchase #7 $119.65   6.664%   $127.6235   $127.62   $127.60   $127.60  
  7 purchase totals = $1,129.60       $1,228.8702   $1,228.87   $1,228.90   $1,228.80