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 $78.63   11.267%   $87.4892   $87.49   $87.50   $87.50  
  Purchase #2 $143.96   9.572%   $157.7399   $157.74   $157.75   $157.70  
  Purchase #3 $239.67   5.210%   $252.1568   $252.16   $252.15   $252.20  
  Purchase #4 $47.88   3.340%   $49.4792   $49.48   $49.50   $49.50  
  Purchase #5 $234.85   9.599%   $257.3933   $257.39   $257.40   $257.40  
  Purchase #6 $204.87   3.799%   $212.653   $212.65   $212.65   $212.70  
  Purchase #7 $231.93   5.181%   $243.9463   $243.95   $243.95   $243.90  
  7 purchase totals = $1,181.79       $1,260.8577   $1,260.86   $1,260.90   $1,260.90