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 $54.99   11.481%   $61.3034   $61.30   $61.30   $61.30  
  Purchase #2 $91.65   6.666%   $97.7594   $97.76   $97.75   $97.80  
  Purchase #3 $238.41   12.794%   $268.9122   $268.91   $268.90   $268.90  
  Purchase #4 $247.65   9.559%   $271.3229   $271.32   $271.30   $271.30  
  Purchase #5 $224.63   12.454%   $252.6054   $252.61   $252.60   $252.60  
  Purchase #6 $223.88   11.282%   $249.1381   $249.14   $249.15   $249.10  
  Purchase #7 $104.85   8.536%   $113.8   $113.80   $113.80   $113.80  
  7 purchase totals = $1,186.06       $1,314.8414   $1,314.84   $1,314.80   $1,314.80