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 $141.45   8.712%   $153.7731   $153.77   $153.75   $153.80  
  Purchase #2 $229.94   6.840%   $245.6679   $245.67   $245.65   $245.70  
  Purchase #3 $152.35   3.511%   $157.699   $157.70   $157.70   $157.70  
  Purchase #4 $23.29   12.333%   $26.1624   $26.16   $26.15   $26.20  
  Purchase #5 $223.57   6.438%   $237.9634   $237.96   $237.95   $238.00  
  Purchase #6 $12.88   10.219%   $14.1962   $14.20   $14.20   $14.20  
  Purchase #7 $58.30   8.562%   $63.2916   $63.29   $63.30   $63.30  
  7 purchase totals = $841.78       $898.7536   $898.75   $898.70   $898.90