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 $101.84   6.289%   $108.2447   $108.24   $108.25   $108.20  
  Purchase #2 $113.97   12.156%   $127.8242   $127.82   $127.80   $127.80  
  Purchase #3 $12.68   11.803%   $14.1766   $14.18   $14.20   $14.20  
  Purchase #4 $184.60   6.831%   $197.21   $197.21   $197.20   $197.20  
  Purchase #5 $32.50   5.372%   $34.2459   $34.25   $34.25   $34.20  
  Purchase #6 $78.68   11.501%   $87.729   $87.73   $87.75   $87.70  
  Purchase #7 $117.64   4.294%   $122.6915   $122.69   $122.70   $122.70  
  7 purchase totals = $641.91       $692.1219   $692.12   $692.15   $692.00