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 $144.65   12.809%   $163.1782   $163.18   $163.20   $163.20  
  Purchase #2 $222.29   4.529%   $232.3575   $232.36   $232.35   $232.40  
  Purchase #3 $31.56   5.497%   $33.2949   $33.29   $33.30   $33.30  
  Purchase #4 $167.41   5.426%   $176.4937   $176.49   $176.50   $176.50  
  Purchase #5 $155.91   13.292%   $176.6336   $176.63   $176.65   $176.60  
  Purchase #6 $188.72   6.765%   $201.4869   $201.49   $201.50   $201.50  
  Purchase #7 $114.25   7.740%   $123.093   $123.09   $123.10   $123.10  
  7 purchase totals = $1,024.79       $1,106.5378   $1,106.53   $1,106.60   $1,106.60