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 $249.53   10.166%   $274.8972   $274.90   $274.90   $274.90  
  Purchase #2 $216.66   9.804%   $237.9013   $237.90   $237.90   $237.90  
  Purchase #3 $101.41   11.844%   $113.421   $113.42   $113.40   $113.40  
  Purchase #4 $24.44   3.521%   $25.3005   $25.30   $25.30   $25.30  
  Purchase #5 $54.73   10.491%   $60.4717   $60.47   $60.45   $60.50  
  Purchase #6 $167.35   7.806%   $180.4133   $180.41   $180.40   $180.40  
  Purchase #7 $123.54   8.727%   $134.3213   $134.32   $134.30   $134.30  
  7 purchase totals = $937.66       $1,026.7263   $1,026.72   $1,026.65   $1,026.70