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 $42.84   4.830%   $44.9092   $44.91   $44.90   $44.90  
  Purchase #2 $109.46   6.292%   $116.3472   $116.35   $116.35   $116.30  
  Purchase #3 $146.45   13.748%   $166.5839   $166.58   $166.60   $166.60  
  Purchase #4 $240.93   6.732%   $257.1494   $257.15   $257.15   $257.10  
  Purchase #5 $61.43   6.872%   $65.6515   $65.65   $65.65   $65.70  
  Purchase #6 $236.99   11.838%   $265.0449   $265.04   $265.05   $265.00  
  Purchase #7 $240.89   9.605%   $264.0275   $264.03   $264.05   $264.00  
  7 purchase totals = $1,078.99       $1,179.7136   $1,179.71   $1,179.75   $1,179.60