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 $51.80   8.546%   $56.2268   $56.23   $56.25   $56.20  
  Purchase #2 $101.74   4.747%   $106.5696   $106.57   $106.55   $106.60  
  Purchase #3 $168.27   7.260%   $180.4864   $180.49   $180.50   $180.50  
  Purchase #4 $151.56   8.468%   $164.3941   $164.39   $164.40   $164.40  
  Purchase #5 $57.41   4.860%   $60.2001   $60.20   $60.20   $60.20  
  Purchase #6 $202.57   4.151%   $210.9787   $210.98   $211.00   $211.00  
  Purchase #7 $32.41   4.220%   $33.7777   $33.78   $33.80   $33.80  
  7 purchase totals = $765.76       $812.6334   $812.64   $812.70   $812.70