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 $61.86   9.258%   $67.587   $67.59   $67.60   $67.60  
  Purchase #2 $51.46   5.567%   $54.3248   $54.32   $54.30   $54.30  
  Purchase #3 $62.91   11.795%   $70.3302   $70.33   $70.35   $70.30  
  Purchase #4 $60.56   10.416%   $66.8679   $66.87   $66.85   $66.90  
  Purchase #5 $213.47   5.243%   $224.6622   $224.66   $224.65   $224.70  
  Purchase #6 $196.94   10.794%   $218.1977   $218.20   $218.20   $218.20  
  Purchase #7 $112.48   5.122%   $118.2412   $118.24   $118.25   $118.20  
  7 purchase totals = $759.68       $820.2110   $820.21   $820.20   $820.20