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 $214.76   7.291%   $230.4182   $230.42   $230.40   $230.40  
  Purchase #2 $158.29   11.273%   $176.134   $176.13   $176.15   $176.10  
  Purchase #3 $66.27   11.363%   $73.8003   $73.80   $73.80   $73.80  
  Purchase #4 $119.75   4.260%   $124.8514   $124.85   $124.85   $124.90  
  Purchase #5 $36.92   11.115%   $41.0237   $41.02   $41.00   $41.00  
  Purchase #6 $226.63   12.221%   $254.3265   $254.33   $254.35   $254.30  
  Purchase #7 $56.96   10.690%   $63.049   $63.05   $63.05   $63.00  
  7 purchase totals = $879.58       $963.6031   $963.60   $963.60   $963.50