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 $241.48   9.510%   $264.4447   $264.44   $264.45   $264.40  
  Purchase #2 $7.89   9.393%   $8.6311   $8.63   $8.65   $8.60  
  Purchase #3 $53.39   12.689%   $60.1647   $60.16   $60.15   $60.20  
  Purchase #4 $58.94   5.248%   $62.0332   $62.03   $62.05   $62.00  
  Purchase #5 $226.39   8.531%   $245.7033   $245.70   $245.70   $245.70  
  Purchase #6 $145.75   13.199%   $164.9875   $164.99   $165.00   $165.00  
  Purchase #7 $42.27   10.689%   $46.7882   $46.79   $46.80   $46.80  
  7 purchase totals = $776.11       $852.7527   $852.74   $852.80   $852.70