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 $238.32   3.871%   $247.5454   $247.55   $247.55   $247.50  
  Purchase #2 $249.52   7.675%   $268.6707   $268.67   $268.65   $268.70  
  Purchase #3 $162.89   13.108%   $184.2416   $184.24   $184.25   $184.20  
  Purchase #4 $54.44   9.189%   $59.4425   $59.44   $59.45   $59.40  
  Purchase #5 $136.54   6.484%   $145.3933   $145.39   $145.40   $145.40  
  Purchase #6 $84.26   11.493%   $93.944   $93.94   $93.95   $93.90  
  Purchase #7 $110.37   13.871%   $125.6794   $125.68   $125.70   $125.70  
  7 purchase totals = $1,036.34       $1,124.9169   $1,124.91   $1,124.95   $1,124.80