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 $226.73   3.837%   $235.4296   $235.43   $235.45   $235.40  
  Purchase #2 $185.75   11.327%   $206.7899   $206.79   $206.80   $206.80  
  Purchase #3 $22.82   4.296%   $23.8003   $23.80   $23.80   $23.80  
  Purchase #4 $54.45   6.454%   $57.9642   $57.96   $57.95   $58.00  
  Purchase #5 $21.54   8.177%   $23.3013   $23.30   $23.30   $23.30  
  Purchase #6 $83.43   5.452%   $87.9786   $87.98   $88.00   $88.00  
  Purchase #7 $177.37   4.829%   $185.9352   $185.94   $185.95   $185.90  
  7 purchase totals = $772.09       $821.1991   $821.20   $821.25   $821.20