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 $207.44   9.323%   $226.7796   $226.78   $226.80   $226.80  
  Purchase #2 $200.37   6.287%   $212.9673   $212.97   $212.95   $213.00  
  Purchase #3 $97.31   3.397%   $100.6156   $100.62   $100.60   $100.60  
  Purchase #4 $186.26   10.855%   $206.4785   $206.48   $206.50   $206.50  
  Purchase #5 $86.33   8.690%   $93.8321   $93.83   $93.85   $93.80  
  Purchase #6 $210.76   9.352%   $230.4703   $230.47   $230.45   $230.50  
  Purchase #7 $175.30   4.841%   $183.7863   $183.79   $183.80   $183.80  
  7 purchase totals = $1,163.77       $1,254.9297   $1,254.94   $1,254.95   $1,255.00