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 $249.41   13.681%   $283.5318   $283.53   $283.55   $283.50  
  Purchase #2 $26.43   4.563%   $27.636   $27.64   $27.65   $27.60  
  Purchase #3 $211.27   4.838%   $221.4912   $221.49   $221.50   $221.50  
  Purchase #4 $61.44   11.695%   $68.6254   $68.63   $68.65   $68.60  
  Purchase #5 $20.31   7.159%   $21.764   $21.76   $21.75   $21.80  
  Purchase #6 $236.78   13.864%   $269.6072   $269.61   $269.60   $269.60  
  Purchase #7 $96.54   12.840%   $108.9357   $108.94   $108.95   $108.90  
  7 purchase totals = $902.18       $1,001.5913   $1,001.60   $1,001.65   $1,001.50