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 $66.92   7.236%   $71.7623   $71.76   $71.75   $71.80  
  Purchase #2 $53.36   3.374%   $55.1604   $55.16   $55.15   $55.20  
  Purchase #3 $212.53   4.114%   $221.2735   $221.27   $221.25   $221.30  
  Purchase #4 $118.62   4.532%   $123.9959   $124.00   $124.00   $124.00  
  Purchase #5 $101.68   11.279%   $113.1485   $113.15   $113.15   $113.10  
  Purchase #6 $66.25   11.786%   $74.0582   $74.06   $74.05   $74.10  
  Purchase #7 $205.42   5.328%   $216.3648   $216.36   $216.35   $216.40  
  7 purchase totals = $824.78       $875.7636   $875.76   $875.70   $875.90