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 $108.81   3.513%   $112.6325   $112.63   $112.65   $112.60  
  Purchase #2 $169.89   8.469%   $184.278   $184.28   $184.30   $184.30  
  Purchase #3 $227.63   4.870%   $238.7156   $238.72   $238.70   $238.70  
  Purchase #4 $67.25   13.194%   $76.123   $76.12   $76.10   $76.10  
  Purchase #5 $198.74   10.298%   $219.2062   $219.21   $219.20   $219.20  
  Purchase #6 $194.55   8.178%   $210.4603   $210.46   $210.45   $210.50  
  Purchase #7 $14.62   6.275%   $15.5374   $15.54   $15.55   $15.50  
  7 purchase totals = $981.49       $1,056.9530   $1,056.96   $1,056.95   $1,056.90