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 $29.78   13.591%   $33.8274   $33.83   $33.85   $33.80  
  Purchase #2 $89.64   4.731%   $93.8809   $93.88   $93.90   $93.90  
  Purchase #3 $119.61   3.319%   $123.5799   $123.58   $123.60   $123.60  
  Purchase #4 $233.65   10.858%   $259.0197   $259.02   $259.00   $259.00  
  Purchase #5 $133.36   6.296%   $141.7563   $141.76   $141.75   $141.80  
  Purchase #6 $45.43   5.666%   $48.0041   $48.00   $48.00   $48.00  
  Purchase #7 $160.42   9.841%   $176.2069   $176.21   $176.20   $176.20  
  7 purchase totals = $811.89       $876.2752   $876.28   $876.30   $876.30