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 $49.25   13.275%   $55.7879   $55.79   $55.80   $55.80  
  Purchase #2 $196.98   6.166%   $209.1258   $209.13   $209.15   $209.10  
  Purchase #3 $204.88   4.192%   $213.4686   $213.47   $213.45   $213.50  
  Purchase #4 $28.76   7.564%   $30.9354   $30.94   $30.95   $30.90  
  Purchase #5 $37.68   3.323%   $38.9321   $38.93   $38.95   $38.90  
  Purchase #6 $207.71   10.367%   $229.2433   $229.24   $229.25   $229.20  
  Purchase #7 $223.93   4.156%   $233.2365   $233.24   $233.25   $233.20  
  7 purchase totals = $949.19       $1,010.7296   $1,010.74   $1,010.80   $1,010.60