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 $80.63   7.302%   $86.5176   $86.52   $86.50   $86.50  
  Purchase #2 $205.93   5.114%   $216.4613   $216.46   $216.45   $216.50  
  Purchase #3 $208.26   13.673%   $236.7354   $236.74   $236.75   $236.70  
  Purchase #4 $229.32   12.451%   $257.8726   $257.87   $257.85   $257.90  
  Purchase #5 $97.75   13.633%   $111.0763   $111.08   $111.10   $111.10  
  Purchase #6 $41.92   7.155%   $44.9194   $44.92   $44.90   $44.90  
  Purchase #7 $79.76   10.148%   $87.854   $87.85   $87.85   $87.90  
  7 purchase totals = $943.57       $1,041.4366   $1,041.44   $1,041.40   $1,041.50