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 $222.71   11.526%   $248.3796   $248.38   $248.40   $248.40  
  Purchase #2 $69.81   10.257%   $76.9704   $76.97   $76.95   $77.00  
  Purchase #3 $23.62   9.408%   $25.8422   $25.84   $25.85   $25.80  
  Purchase #4 $245.54   12.443%   $276.0925   $276.09   $276.10   $276.10  
  Purchase #5 $91.27   4.727%   $95.5843   $95.58   $95.60   $95.60  
  Purchase #6 $82.34   9.401%   $90.0808   $90.08   $90.10   $90.10  
  Purchase #7 $231.53   4.484%   $241.9118   $241.91   $241.90   $241.90  
  7 purchase totals = $966.82       $1,054.8616   $1,054.85   $1,054.90   $1,054.90