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 $225.32   4.718%   $235.9506   $235.95   $235.95   $236.00  
  Purchase #2 $57.99   3.339%   $59.9263   $59.93   $59.95   $59.90  
  Purchase #3 $125.44   7.866%   $135.3071   $135.31   $135.30   $135.30  
  Purchase #4 $142.91   3.201%   $147.4845   $147.48   $147.50   $147.50  
  Purchase #5 $144.91   7.849%   $156.284   $156.28   $156.30   $156.30  
  Purchase #6 $169.39   5.530%   $178.7573   $178.76   $178.75   $178.80  
  Purchase #7 $85.66   7.390%   $91.9903   $91.99   $92.00   $92.00  
  7 purchase totals = $951.62       $1,005.7001   $1,005.70   $1,005.75   $1,005.80