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 $174.56   12.671%   $196.6785   $196.68   $196.70   $196.70  
  Purchase #2 $224.71   9.468%   $245.9855   $245.99   $246.00   $246.00  
  Purchase #3 $218.91   7.525%   $235.383   $235.38   $235.40   $235.40  
  Purchase #4 $59.84   13.581%   $67.9669   $67.97   $67.95   $68.00  
  Purchase #5 $148.47   6.259%   $157.7627   $157.76   $157.75   $157.80  
  Purchase #6 $84.66   13.354%   $95.9655   $95.97   $95.95   $96.00  
  Purchase #7 $180.26   12.852%   $203.427   $203.43   $203.45   $203.40  
  7 purchase totals = $1,091.41       $1,203.1691   $1,203.18   $1,203.20   $1,203.30