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 $167.97   13.823%   $191.1885   $191.19   $191.20   $191.20  
  Purchase #2 $58.71   9.572%   $64.3297   $64.33   $64.35   $64.30  
  Purchase #3 $173.34   3.682%   $179.7224   $179.72   $179.70   $179.70  
  Purchase #4 $95.66   10.551%   $105.7531   $105.75   $105.75   $105.80  
  Purchase #5 $30.87   13.728%   $35.1078   $35.11   $35.10   $35.10  
  Purchase #6 $88.77   3.661%   $92.0199   $92.02   $92.00   $92.00  
  Purchase #7 $90.72   8.135%   $98.1001   $98.10   $98.10   $98.10  
  7 purchase totals = $706.04       $766.2215   $766.22   $766.20   $766.20