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 $152.63   8.623%   $165.7913   $165.79   $165.80   $165.80  
  Purchase #2 $235.27   10.225%   $259.3264   $259.33   $259.35   $259.30  
  Purchase #3 $71.89   11.399%   $80.0847   $80.08   $80.10   $80.10  
  Purchase #4 $186.62   5.792%   $197.429   $197.43   $197.45   $197.40  
  Purchase #5 $248.78   8.750%   $270.5483   $270.55   $270.55   $270.50  
  Purchase #6 $156.26   12.236%   $175.38   $175.38   $175.40   $175.40  
  Purchase #7 $93.26   11.663%   $104.1369   $104.14   $104.15   $104.10  
  7 purchase totals = $1,144.71       $1,252.6966   $1,252.70   $1,252.80   $1,252.60