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 $64.65   13.221%   $73.1974   $73.20   $73.20   $73.20  
  Purchase #2 $144.87   11.478%   $161.4982   $161.50   $161.50   $161.50  
  Purchase #3 $123.70   12.797%   $139.5299   $139.53   $139.55   $139.50  
  Purchase #4 $194.59   13.865%   $221.5699   $221.57   $221.55   $221.60  
  Purchase #5 $86.65   8.565%   $94.0716   $94.07   $94.05   $94.10  
  Purchase #6 $22.88   8.559%   $24.8383   $24.84   $24.85   $24.80  
  Purchase #7 $21.54   13.331%   $24.4115   $24.41   $24.40   $24.40  
  7 purchase totals = $658.88       $739.1168   $739.12   $739.10   $739.10