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 $56.39   13.413%   $63.9536   $63.95   $63.95   $64.00  
  Purchase #2 $162.25   3.452%   $167.8509   $167.85   $167.85   $167.90  
  Purchase #3 $97.33   4.581%   $101.7887   $101.79   $101.80   $101.80  
  Purchase #4 $229.28   3.827%   $238.0545   $238.05   $238.05   $238.10  
  Purchase #5 $124.25   9.159%   $135.6301   $135.63   $135.65   $135.60  
  Purchase #6 $134.75   11.230%   $149.8824   $149.88   $149.90   $149.90  
  Purchase #7 $235.55   5.298%   $248.0294   $248.03   $248.05   $248.00  
  7 purchase totals = $1,039.80       $1,105.1896   $1,105.18   $1,105.25   $1,105.30