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 $203.42   8.663%   $221.0423   $221.04   $221.05   $221.00  
  Purchase #2 $81.93   13.267%   $92.7997   $92.80   $92.80   $92.80  
  Purchase #3 $114.56   9.717%   $125.6918   $125.69   $125.70   $125.70  
  Purchase #4 $249.73   12.841%   $281.7978   $281.80   $281.80   $281.80  
  Purchase #5 $221.52   11.512%   $247.0214   $247.02   $247.00   $247.00  
  Purchase #6 $66.47   4.582%   $69.5157   $69.52   $69.50   $69.50  
  Purchase #7 $125.68   4.820%   $131.7378   $131.74   $131.75   $131.70  
  7 purchase totals = $1,063.31       $1,169.6065   $1,169.61   $1,169.60   $1,169.50