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 $38.83   12.623%   $43.7315   $43.73   $43.75   $43.70  
  Purchase #2 $114.58   13.708%   $130.2866   $130.29   $130.30   $130.30  
  Purchase #3 $30.81   13.464%   $34.9583   $34.96   $34.95   $35.00  
  Purchase #4 $40.74   9.617%   $44.658   $44.66   $44.65   $44.70  
  Purchase #5 $68.76   7.159%   $73.6825   $73.68   $73.70   $73.70  
  Purchase #6 $33.89   7.782%   $36.5273   $36.53   $36.55   $36.50  
  Purchase #7 $9.61   6.111%   $10.1973   $10.20   $10.20   $10.20  
  7 purchase totals = $337.22       $374.0415   $374.05   $374.10   $374.10