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 $209.38   7.806%   $225.7242   $225.72   $225.70   $225.70  
  Purchase #2 $221.40   11.449%   $246.7481   $246.75   $246.75   $246.70  
  Purchase #3 $200.37   4.824%   $210.0358   $210.04   $210.05   $210.00  
  Purchase #4 $23.27   6.125%   $24.6953   $24.70   $24.70   $24.70  
  Purchase #5 $229.56   5.428%   $242.0205   $242.02   $242.00   $242.00  
  Purchase #6 $5.80   11.400%   $6.4612   $6.46   $6.45   $6.50  
  Purchase #7 $5.91   12.728%   $6.6622   $6.66   $6.65   $6.70  
  7 purchase totals = $895.69       $962.3473   $962.35   $962.30   $962.30