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 $225.47   9.438%   $246.7499   $246.75   $246.75   $246.70  
  Purchase #2 $241.79   9.259%   $264.1773   $264.18   $264.20   $264.20  
  Purchase #3 $85.76   11.636%   $95.739   $95.74   $95.75   $95.70  
  Purchase #4 $120.93   5.448%   $127.5183   $127.52   $127.50   $127.50  
  Purchase #5 $124.55   7.527%   $133.9249   $133.92   $133.90   $133.90  
  Purchase #6 $8.66   9.345%   $9.4693   $9.47   $9.45   $9.50  
  Purchase #7 $176.69   6.287%   $187.7985   $187.80   $187.80   $187.80  
  7 purchase totals = $983.85       $1,065.3772   $1,065.38   $1,065.35   $1,065.30