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 $68.78   5.851%   $72.8043   $72.80   $72.80   $72.80  
  Purchase #2 $128.62   12.454%   $144.6383   $144.64   $144.65   $144.60  
  Purchase #3 $239.54   6.324%   $254.6885   $254.69   $254.70   $254.70  
  Purchase #4 $195.65   3.614%   $202.7208   $202.72   $202.70   $202.70  
  Purchase #5 $115.27   11.830%   $128.9064   $128.91   $128.90   $128.90  
  Purchase #6 $125.85   4.873%   $131.9827   $131.98   $132.00   $132.00  
  Purchase #7 $66.77   13.314%   $75.6598   $75.66   $75.65   $75.70  
  7 purchase totals = $940.48       $1,011.4008   $1,011.40   $1,011.40   $1,011.40