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 $62.32   11.238%   $69.3235   $69.32   $69.30   $69.30  
  Purchase #2 $206.74   9.423%   $226.2211   $226.22   $226.20   $226.20  
  Purchase #3 $18.91   13.334%   $21.4315   $21.43   $21.45   $21.40  
  Purchase #4 $59.90   4.459%   $62.5709   $62.57   $62.55   $62.60  
  Purchase #5 $188.69   9.573%   $206.7533   $206.75   $206.75   $206.80  
  Purchase #6 $33.85   4.244%   $35.2866   $35.29   $35.30   $35.30  
  Purchase #7 $62.37   11.710%   $69.6735   $69.67   $69.65   $69.70  
  7 purchase totals = $632.78       $691.2604   $691.25   $691.20   $691.30