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 $22.46   6.684%   $23.9612   $23.96   $23.95   $24.00  
  Purchase #2 $228.69   9.817%   $251.1405   $251.14   $251.15   $251.10  
  Purchase #3 $210.27   6.524%   $223.988   $223.99   $224.00   $224.00  
  Purchase #4 $145.47   13.523%   $165.1419   $165.14   $165.15   $165.10  
  Purchase #5 $66.43   11.791%   $74.2628   $74.26   $74.25   $74.30  
  Purchase #6 $177.60   5.342%   $187.0874   $187.09   $187.10   $187.10  
  Purchase #7 $6.90   9.706%   $7.5697   $7.57   $7.55   $7.60  
  7 purchase totals = $857.82       $933.1515   $933.15   $933.15   $933.20