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 $60.78   13.377%   $68.9105   $68.91   $68.90   $68.90  
  Purchase #2 $93.78   9.472%   $102.6628   $102.66   $102.65   $102.70  
  Purchase #3 $9.95   11.676%   $11.1118   $11.11   $11.10   $11.10  
  Purchase #4 $230.78   12.574%   $259.7983   $259.80   $259.80   $259.80  
  Purchase #5 $93.49   6.784%   $99.8324   $99.83   $99.85   $99.80  
  Purchase #6 $224.74   13.874%   $255.9204   $255.92   $255.90   $255.90  
  Purchase #7 $226.92   10.161%   $249.9773   $249.98   $250.00   $250.00  
  7 purchase totals = $940.44       $1,048.2135   $1,048.21   $1,048.20   $1,048.20