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 $240.75   5.471%   $253.9214   $253.92   $253.90   $253.90  
  Purchase #2 $45.54   4.801%   $47.7264   $47.73   $47.75   $47.70  
  Purchase #3 $58.30   5.454%   $61.4797   $61.48   $61.50   $61.50  
  Purchase #4 $119.86   5.135%   $126.0148   $126.01   $126.00   $126.00  
  Purchase #5 $220.71   11.697%   $246.5264   $246.53   $246.55   $246.50  
  Purchase #6 $203.54   9.189%   $222.2433   $222.24   $222.25   $222.20  
  Purchase #7 $156.25   5.541%   $164.9078   $164.91   $164.90   $164.90  
  7 purchase totals = $1,044.95       $1,122.8198   $1,122.82   $1,122.85   $1,122.70