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 $55.67   9.802%   $61.1268   $61.13   $61.15   $61.10  
  Purchase #2 $248.44   11.165%   $276.1783   $276.18   $276.20   $276.20  
  Purchase #3 $192.73   7.582%   $207.3428   $207.34   $207.35   $207.30  
  Purchase #4 $185.91   3.823%   $193.0173   $193.02   $193.00   $193.00  
  Purchase #5 $23.97   9.671%   $26.2881   $26.29   $26.30   $26.30  
  Purchase #6 $134.92   12.691%   $152.0427   $152.04   $152.05   $152.00  
  Purchase #7 $129.82   12.653%   $146.2461   $146.25   $146.25   $146.20  
  7 purchase totals = $971.46       $1,062.2421   $1,062.25   $1,062.30   $1,062.10