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 $205.65   6.315%   $218.6368   $218.64   $218.65   $218.60  
  Purchase #2 $117.43   4.449%   $122.6545   $122.65   $122.65   $122.70  
  Purchase #3 $17.27   5.764%   $18.2654   $18.27   $18.25   $18.30  
  Purchase #4 $242.85   8.699%   $263.9755   $263.98   $264.00   $264.00  
  Purchase #5 $232.92   9.377%   $254.7609   $254.76   $254.75   $254.80  
  Purchase #6 $206.30   9.682%   $226.274   $226.27   $226.25   $226.30  
  Purchase #7 $241.78   4.536%   $252.7471   $252.75   $252.75   $252.70  
  7 purchase totals = $1,264.20       $1,357.3142   $1,357.32   $1,357.30   $1,357.40