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 $72.86   5.113%   $76.5853   $76.59   $76.60   $76.60  
  Purchase #2 $223.54   12.419%   $251.3014   $251.30   $251.30   $251.30  
  Purchase #3 $217.66   4.242%   $226.8931   $226.89   $226.90   $226.90  
  Purchase #4 $197.87   13.853%   $225.2809   $225.28   $225.30   $225.30  
  Purchase #5 $80.96   12.860%   $91.3715   $91.37   $91.35   $91.40  
  Purchase #6 $59.88   12.821%   $67.5572   $67.56   $67.55   $67.60  
  Purchase #7 $13.44   13.235%   $15.2188   $15.22   $15.20   $15.20  
  7 purchase totals = $866.21       $954.2082   $954.21   $954.20   $954.30