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 $56.67   9.329%   $61.9567   $61.96   $61.95   $62.00  
  Purchase #2 $84.57   13.572%   $96.0478   $96.05   $96.05   $96.00  
  Purchase #3 $37.51   11.247%   $41.7287   $41.73   $41.75   $41.70  
  Purchase #4 $241.43   11.498%   $269.1896   $269.19   $269.20   $269.20  
  Purchase #5 $227.78   6.325%   $242.1871   $242.19   $242.20   $242.20  
  Purchase #6 $205.45   8.172%   $222.2394   $222.24   $222.25   $222.20  
  Purchase #7 $50.43   6.287%   $53.6005   $53.60   $53.60   $53.60  
  7 purchase totals = $903.84       $986.9498   $986.96   $987.00   $986.90