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 $223.72   11.135%   $248.6312   $248.63   $248.65   $248.60  
  Purchase #2 $173.55   3.629%   $179.8481   $179.85   $179.85   $179.80  
  Purchase #3 $199.28   10.632%   $220.4674   $220.47   $220.45   $220.50  
  Purchase #4 $44.75   4.762%   $46.881   $46.88   $46.90   $46.90  
  Purchase #5 $130.96   13.814%   $149.0508   $149.05   $149.05   $149.10  
  Purchase #6 $226.26   12.302%   $254.0945   $254.09   $254.10   $254.10  
  Purchase #7 $247.42   5.411%   $260.8079   $260.81   $260.80   $260.80  
  7 purchase totals = $1,245.94       $1,359.7809   $1,359.78   $1,359.80   $1,359.80