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 $83.71   12.861%   $94.4759   $94.48   $94.50   $94.50  
  Purchase #2 $24.99   7.507%   $26.866   $26.87   $26.85   $26.90  
  Purchase #3 $69.74   5.199%   $73.3658   $73.37   $73.35   $73.40  
  Purchase #4 $60.66   3.314%   $62.6703   $62.67   $62.65   $62.70  
  Purchase #5 $38.39   9.416%   $42.0048   $42.00   $42.00   $42.00  
  Purchase #6 $108.57   4.403%   $113.3503   $113.35   $113.35   $113.40  
  Purchase #7 $119.36   3.297%   $123.2953   $123.30   $123.30   $123.30  
  7 purchase totals = $505.42       $536.0284   $536.04   $536.00   $536.20