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 $75.38   11.519%   $84.063   $84.06   $84.05   $84.10  
  Purchase #2 $120.82   5.501%   $127.4663   $127.47   $127.45   $127.50  
  Purchase #3 $239.85   9.680%   $263.0675   $263.07   $263.05   $263.10  
  Purchase #4 $157.66   9.680%   $172.9215   $172.92   $172.90   $172.90  
  Purchase #5 $176.48   9.639%   $193.4909   $193.49   $193.50   $193.50  
  Purchase #6 $217.84   8.208%   $235.7203   $235.72   $235.70   $235.70  
  Purchase #7 $44.81   4.141%   $46.6656   $46.67   $46.65   $46.70  
  7 purchase totals = $1,032.84       $1,123.3951   $1,123.40   $1,123.30   $1,123.50