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 $68.50   8.293%   $74.1807   $74.18   $74.20   $74.20  
  Purchase #2 $213.58   12.541%   $240.3651   $240.37   $240.35   $240.40  
  Purchase #3 $76.66   12.219%   $86.0271   $86.03   $86.05   $86.00  
  Purchase #4 $83.30   8.831%   $90.6562   $90.66   $90.65   $90.70  
  Purchase #5 $155.45   4.438%   $162.3489   $162.35   $162.35   $162.30  
  Purchase #6 $67.53   6.782%   $72.1099   $72.11   $72.10   $72.10  
  Purchase #7 $122.48   5.488%   $129.2017   $129.20   $129.20   $129.20  
  7 purchase totals = $787.50       $854.8896   $854.90   $854.90   $854.90