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 $57.25   11.811%   $64.0118   $64.01   $64.00   $64.00  
  Purchase #2 $249.49   11.532%   $278.2612   $278.26   $278.25   $278.30  
  Purchase #3 $109.66   13.292%   $124.236   $124.24   $124.25   $124.20  
  Purchase #4 $21.55   4.715%   $22.5661   $22.57   $22.55   $22.60  
  Purchase #5 $225.27   12.369%   $253.1336   $253.13   $253.15   $253.10  
  Purchase #6 $194.37   9.509%   $212.8526   $212.85   $212.85   $212.90  
  Purchase #7 $72.79   11.348%   $81.0502   $81.05   $81.05   $81.10  
  7 purchase totals = $930.38       $1,036.1115   $1,036.11   $1,036.10   $1,036.20