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 $218.80   12.731%   $246.6554   $246.66   $246.65   $246.70  
  Purchase #2 $45.27   6.606%   $48.2605   $48.26   $48.25   $48.30  
  Purchase #3 $234.54   8.706%   $254.9591   $254.96   $254.95   $255.00  
  Purchase #4 $165.32   6.312%   $175.755   $175.76   $175.75   $175.80  
  Purchase #5 $170.53   8.425%   $184.8972   $184.90   $184.90   $184.90  
  Purchase #6 $131.62   10.523%   $145.4704   $145.47   $145.45   $145.50  
  Purchase #7 $174.94   9.541%   $191.631   $191.63   $191.65   $191.60  
  7 purchase totals = $1,141.02       $1,247.6286   $1,247.64   $1,247.60   $1,247.80