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 $197.85   6.121%   $209.9604   $209.96   $209.95   $210.00  
  Purchase #2 $141.68   7.172%   $151.8413   $151.84   $151.85   $151.80  
  Purchase #3 $62.71   3.538%   $64.9287   $64.93   $64.95   $64.90  
  Purchase #4 $148.28   5.388%   $156.2693   $156.27   $156.25   $156.30  
  Purchase #5 $130.64   12.620%   $147.1268   $147.13   $147.15   $147.10  
  Purchase #6 $48.52   13.584%   $55.111   $55.11   $55.10   $55.10  
  Purchase #7 $70.82   5.192%   $74.497   $74.50   $74.50   $74.50  
  7 purchase totals = $800.50       $859.7345   $859.74   $859.75   $859.70