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 $88.90   4.784%   $93.153   $93.15   $93.15   $93.20  
  Purchase #2 $91.83   12.163%   $102.9993   $103.00   $103.00   $103.00  
  Purchase #3 $97.54   4.252%   $101.6874   $101.69   $101.70   $101.70  
  Purchase #4 $79.27   4.355%   $82.7222   $82.72   $82.70   $82.70  
  Purchase #5 $195.61   12.242%   $219.5566   $219.56   $219.55   $219.60  
  Purchase #6 $163.86   5.373%   $172.6642   $172.66   $172.65   $172.70  
  Purchase #7 $62.34   4.526%   $65.1615   $65.16   $65.15   $65.20  
  7 purchase totals = $779.35       $837.9442   $837.94   $837.90   $838.10