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 $184.76   10.714%   $204.5552   $204.56   $204.55   $204.60  
  Purchase #2 $57.30   7.391%   $61.535   $61.54   $61.55   $61.50  
  Purchase #3 $24.58   7.851%   $26.5098   $26.51   $26.50   $26.50  
  Purchase #4 $246.78   10.204%   $271.9614   $271.96   $271.95   $272.00  
  Purchase #5 $114.31   10.840%   $126.7012   $126.70   $126.70   $126.70  
  Purchase #6 $165.36   5.503%   $174.4598   $174.46   $174.45   $174.50  
  Purchase #7 $234.82   6.403%   $249.8555   $249.86   $249.85   $249.90  
  7 purchase totals = $1,027.91       $1,115.5779   $1,115.59   $1,115.55   $1,115.70