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 $241.49   5.709%   $255.2767   $255.28   $255.30   $255.30  
  Purchase #2 $210.94   13.316%   $239.0288   $239.03   $239.05   $239.00  
  Purchase #3 $52.31   4.713%   $54.7754   $54.78   $54.80   $54.80  
  Purchase #4 $162.68   3.223%   $167.9232   $167.92   $167.90   $167.90  
  Purchase #5 $155.25   10.502%   $171.5544   $171.55   $171.55   $171.60  
  Purchase #6 $140.95   10.337%   $155.52   $155.52   $155.50   $155.50  
  Purchase #7 $73.59   11.154%   $81.7982   $81.80   $81.80   $81.80  
  7 purchase totals = $1,037.21       $1,125.8767   $1,125.88   $1,125.90   $1,125.90