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 $245.91   8.771%   $267.4788   $267.48   $267.50   $267.50  
  Purchase #2 $218.77   12.274%   $245.6218   $245.62   $245.60   $245.60  
  Purchase #3 $25.88   12.454%   $29.1031   $29.10   $29.10   $29.10  
  Purchase #4 $208.69   8.474%   $226.3744   $226.37   $226.35   $226.40  
  Purchase #5 $89.69   5.366%   $94.5028   $94.50   $94.50   $94.50  
  Purchase #6 $72.77   8.727%   $79.1206   $79.12   $79.10   $79.10  
  Purchase #7 $203.66   12.668%   $229.4596   $229.46   $229.45   $229.50  
  7 purchase totals = $1,065.37       $1,171.6611   $1,171.65   $1,171.60   $1,171.70