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 $34.83   5.663%   $36.8024   $36.80   $36.80   $36.80  
  Purchase #2 $95.34   9.806%   $104.689   $104.69   $104.70   $104.70  
  Purchase #3 $61.49   3.411%   $63.5874   $63.59   $63.60   $63.60  
  Purchase #4 $236.77   7.839%   $255.3304   $255.33   $255.35   $255.30  
  Purchase #5 $162.60   12.742%   $183.3185   $183.32   $183.30   $183.30  
  Purchase #6 $21.72   9.851%   $23.8596   $23.86   $23.85   $23.90  
  Purchase #7 $76.59   3.336%   $79.145   $79.15   $79.15   $79.10  
  7 purchase totals = $689.34       $746.7323   $746.74   $746.75   $746.70