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 $60.43   12.586%   $68.0357   $68.04   $68.05   $68.00  
  Purchase #2 $131.54   11.857%   $147.1367   $147.14   $147.15   $147.10  
  Purchase #3 $193.66   8.421%   $209.9681   $209.97   $209.95   $210.00  
  Purchase #4 $226.73   10.211%   $249.8814   $249.88   $249.90   $249.90  
  Purchase #5 $235.33   13.874%   $267.9797   $267.98   $268.00   $268.00  
  Purchase #6 $83.65   8.652%   $90.8874   $90.89   $90.90   $90.90  
  Purchase #7 $145.91   13.538%   $165.6633   $165.66   $165.65   $165.70  
  7 purchase totals = $1,077.25       $1,199.5523   $1,199.56   $1,199.60   $1,199.60