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 $84.68   9.316%   $92.5688   $92.57   $92.55   $92.60  
  Purchase #2 $228.83   13.488%   $259.6946   $259.69   $259.70   $259.70  
  Purchase #3 $249.94   5.743%   $264.2941   $264.29   $264.30   $264.30  
  Purchase #4 $39.68   9.850%   $43.5885   $43.59   $43.60   $43.60  
  Purchase #5 $193.44   4.108%   $201.3865   $201.39   $201.40   $201.40  
  Purchase #6 $115.45   11.630%   $128.8768   $128.88   $128.90   $128.90  
  Purchase #7 $75.79   6.870%   $80.9968   $81.00   $81.00   $81.00  
  7 purchase totals = $987.81       $1,071.4061   $1,071.41   $1,071.45   $1,071.50