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 $239.65   8.595%   $260.2479   $260.25   $260.25   $260.20  
  Purchase #2 $114.43   5.511%   $120.7362   $120.74   $120.75   $120.70  
  Purchase #3 $79.74   8.711%   $86.6862   $86.69   $86.70   $86.70  
  Purchase #4 $15.38   4.750%   $16.1106   $16.11   $16.10   $16.10  
  Purchase #5 $125.73   11.689%   $140.4266   $140.43   $140.45   $140.40  
  Purchase #6 $169.52   3.758%   $175.8906   $175.89   $175.90   $175.90  
  Purchase #7 $236.95   6.436%   $252.2001   $252.20   $252.20   $252.20  
  7 purchase totals = $981.40       $1,052.2982   $1,052.31   $1,052.35   $1,052.20