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 $206.74   3.751%   $214.4948   $214.49   $214.50   $214.50  
  Purchase #2 $8.92   9.219%   $9.7423   $9.74   $9.75   $9.70  
  Purchase #3 $182.93   9.124%   $199.6205   $199.62   $199.60   $199.60  
  Purchase #4 $96.35   11.715%   $107.6374   $107.64   $107.65   $107.60  
  Purchase #5 $115.27   10.128%   $126.9445   $126.94   $126.95   $126.90  
  Purchase #6 $142.31   4.323%   $148.4621   $148.46   $148.45   $148.50  
  Purchase #7 $47.76   6.828%   $51.0211   $51.02   $51.00   $51.00  
  7 purchase totals = $800.28       $857.9227   $857.91   $857.90   $857.80