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 $62.35   3.349%   $64.4381   $64.44   $64.45   $64.40  
  Purchase #2 $9.68   11.292%   $10.7731   $10.77   $10.75   $10.80  
  Purchase #3 $128.82   3.234%   $132.986   $132.99   $133.00   $133.00  
  Purchase #4 $166.80   13.449%   $189.2329   $189.23   $189.25   $189.20  
  Purchase #5 $80.51   9.201%   $87.9177   $87.92   $87.90   $87.90  
  Purchase #6 $204.37   8.387%   $221.5105   $221.51   $221.50   $221.50  
  Purchase #7 $90.50   6.423%   $96.3128   $96.31   $96.30   $96.30  
  7 purchase totals = $743.03       $803.1711   $803.17   $803.15   $803.10