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 $238.56   10.664%   $264   $264.00   $264.00   $264.00  
  Purchase #2 $212.94   5.606%   $224.8774   $224.88   $224.90   $224.90  
  Purchase #3 $20.66   8.589%   $22.4345   $22.43   $22.45   $22.40  
  Purchase #4 $235.66   12.715%   $265.6242   $265.62   $265.60   $265.60  
  Purchase #5 $117.33   10.157%   $129.2472   $129.25   $129.25   $129.20  
  Purchase #6 $23.86   4.737%   $24.9902   $24.99   $25.00   $25.00  
  Purchase #7 $120.95   11.355%   $134.6839   $134.68   $134.70   $134.70  
  7 purchase totals = $969.96       $1,065.8574   $1,065.85   $1,065.90   $1,065.80