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 $61.25   12.487%   $68.8983   $68.90   $68.90   $68.90  
  Purchase #2 $95.60   9.373%   $104.5606   $104.56   $104.55   $104.60  
  Purchase #3 $160.63   6.737%   $171.4516   $171.45   $171.45   $171.50  
  Purchase #4 $129.27   11.384%   $143.9861   $143.99   $144.00   $144.00  
  Purchase #5 $83.68   7.239%   $89.7376   $89.74   $89.75   $89.70  
  Purchase #6 $152.98   6.108%   $162.324   $162.32   $162.30   $162.30  
  Purchase #7 $71.28   13.163%   $80.6626   $80.66   $80.65   $80.70  
  7 purchase totals = $754.69       $821.6208   $821.62   $821.60   $821.70