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 $83.80   11.586%   $93.5091   $93.51   $93.50   $93.50  
  Purchase #2 $138.70   5.675%   $146.5712   $146.57   $146.55   $146.60  
  Purchase #3 $231.34   13.290%   $262.0851   $262.09   $262.10   $262.10  
  Purchase #4 $113.57   4.791%   $119.0111   $119.01   $119.00   $119.00  
  Purchase #5 $203.88   4.638%   $213.336   $213.34   $213.35   $213.30  
  Purchase #6 $208.68   12.175%   $234.0868   $234.09   $234.10   $234.10  
  Purchase #7 $176.76   12.265%   $198.4396   $198.44   $198.45   $198.40  
  7 purchase totals = $1,156.73       $1,267.0389   $1,267.05   $1,267.05   $1,267.00