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 $102.42   12.242%   $114.9583   $114.96   $114.95   $115.00  
  Purchase #2 $129.56   6.315%   $137.7417   $137.74   $137.75   $137.70  
  Purchase #3 $175.79   7.107%   $188.2834   $188.28   $188.30   $188.30  
  Purchase #4 $193.82   3.334%   $200.282   $200.28   $200.30   $200.30  
  Purchase #5 $153.90   6.197%   $163.4372   $163.44   $163.45   $163.40  
  Purchase #6 $68.65   10.691%   $75.9894   $75.99   $76.00   $76.00  
  Purchase #7 $144.99   7.820%   $156.3282   $156.33   $156.35   $156.30  
  7 purchase totals = $969.13       $1,037.0202   $1,037.02   $1,037.10   $1,037.00