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 $68.85   8.655%   $74.809   $74.81   $74.80   $74.80  
  Purchase #2 $120.51   4.538%   $125.9787   $125.98   $126.00   $126.00  
  Purchase #3 $53.41   11.806%   $59.7156   $59.72   $59.70   $59.70  
  Purchase #4 $205.54   5.205%   $216.2384   $216.24   $216.25   $216.20  
  Purchase #5 $14.39   4.298%   $15.0085   $15.01   $15.00   $15.00  
  Purchase #6 $131.41   4.781%   $137.6927   $137.69   $137.70   $137.70  
  Purchase #7 $20.84   8.189%   $22.5466   $22.55   $22.55   $22.50  
  7 purchase totals = $614.95       $651.9895   $652.00   $652.00   $651.90