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 $73.82   12.810%   $83.2763   $83.28   $83.30   $83.30  
  Purchase #2 $23.39   5.302%   $24.6301   $24.63   $24.65   $24.60  
  Purchase #3 $39.62   10.830%   $43.9108   $43.91   $43.90   $43.90  
  Purchase #4 $138.66   9.811%   $152.2639   $152.26   $152.25   $152.30  
  Purchase #5 $158.68   10.193%   $174.8543   $174.85   $174.85   $174.90  
  Purchase #6 $228.38   3.411%   $236.17   $236.17   $236.15   $236.20  
  Purchase #7 $77.82   3.309%   $80.3951   $80.40   $80.40   $80.40  
  7 purchase totals = $740.37       $795.5005   $795.50   $795.50   $795.60