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 $91.71   5.658%   $96.899   $96.90   $96.90   $96.90  
  Purchase #2 $171.66   6.368%   $182.5913   $182.59   $182.60   $182.60  
  Purchase #3 $66.74   7.850%   $71.9791   $71.98   $72.00   $72.00  
  Purchase #4 $129.45   13.289%   $146.6526   $146.65   $146.65   $146.70  
  Purchase #5 $13.97   4.655%   $14.6203   $14.62   $14.60   $14.60  
  Purchase #6 $213.82   3.397%   $221.0835   $221.08   $221.10   $221.10  
  Purchase #7 $131.25   13.528%   $149.0055   $149.01   $149.00   $149.00  
  7 purchase totals = $818.60       $882.8313   $882.83   $882.85   $882.90