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 $101.74   5.399%   $107.2329   $107.23   $107.25   $107.20  
  Purchase #2 $241.81   12.208%   $271.3302   $271.33   $271.35   $271.30  
  Purchase #3 $40.73   7.589%   $43.821   $43.82   $43.80   $43.80  
  Purchase #4 $44.47   9.516%   $48.7018   $48.70   $48.70   $48.70  
  Purchase #5 $70.44   5.369%   $74.2219   $74.22   $74.20   $74.20  
  Purchase #6 $172.63   12.312%   $193.8842   $193.88   $193.90   $193.90  
  Purchase #7 $235.70   11.480%   $262.7584   $262.76   $262.75   $262.80  
  7 purchase totals = $907.52       $1,001.9504   $1,001.94   $1,001.95   $1,001.90