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 $248.47   5.804%   $262.8912   $262.89   $262.90   $262.90  
  Purchase #2 $189.85   6.257%   $201.7289   $201.73   $201.75   $201.70  
  Purchase #3 $50.83   8.277%   $55.0372   $55.04   $55.05   $55.00  
  Purchase #4 $114.94   11.585%   $128.2558   $128.26   $128.25   $128.30  
  Purchase #5 $204.71   12.183%   $229.6498   $229.65   $229.65   $229.60  
  Purchase #6 $81.75   11.661%   $91.2829   $91.28   $91.30   $91.30  
  Purchase #7 $225.73   10.671%   $249.8176   $249.82   $249.80   $249.80  
  7 purchase totals = $1,116.28       $1,218.6634   $1,218.67   $1,218.70   $1,218.60