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 $55.63   8.406%   $60.3063   $60.31   $60.30   $60.30  
  Purchase #2 $207.87   6.700%   $221.7973   $221.80   $221.80   $221.80  
  Purchase #3 $45.84   3.113%   $47.267   $47.27   $47.25   $47.30  
  Purchase #4 $195.78   13.287%   $221.7933   $221.79   $221.80   $221.80  
  Purchase #5 $240.99   6.473%   $256.5893   $256.59   $256.60   $256.60  
  Purchase #6 $154.83   7.814%   $166.9284   $166.93   $166.95   $166.90  
  Purchase #7 $78.31   7.748%   $84.3775   $84.38   $84.40   $84.40  
  7 purchase totals = $979.25       $1,059.0591   $1,059.07   $1,059.10   $1,059.10