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 $146.75   12.422%   $164.9793   $164.98   $165.00   $165.00  
  Purchase #2 $166.43   9.344%   $181.9812   $181.98   $182.00   $182.00  
  Purchase #3 $126.75   8.521%   $137.5504   $137.55   $137.55   $137.60  
  Purchase #4 $141.29   12.530%   $158.9936   $158.99   $159.00   $159.00  
  Purchase #5 $55.64   7.121%   $59.6021   $59.60   $59.60   $59.60  
  Purchase #6 $9.55   6.793%   $10.1987   $10.20   $10.20   $10.20  
  Purchase #7 $247.69   12.226%   $277.9726   $277.97   $277.95   $278.00  
  7 purchase totals = $894.10       $991.2779   $991.27   $991.30   $991.40