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 $216.99   12.365%   $243.8208   $243.82   $243.80   $243.80  
  Purchase #2 $183.43   9.874%   $201.5419   $201.54   $201.55   $201.50  
  Purchase #3 $240.89   12.641%   $271.3409   $271.34   $271.35   $271.30  
  Purchase #4 $94.32   4.412%   $98.4814   $98.48   $98.50   $98.50  
  Purchase #5 $244.64   5.758%   $258.7264   $258.73   $258.75   $258.70  
  Purchase #6 $219.55   12.509%   $247.0135   $247.01   $247.00   $247.00  
  Purchase #7 $40.73   6.784%   $43.4931   $43.49   $43.50   $43.50  
  7 purchase totals = $1,240.55       $1,364.4180   $1,364.41   $1,364.45   $1,364.30