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 $26.26   11.142%   $29.1859   $29.19   $29.20   $29.20  
  Purchase #2 $192.48   9.743%   $211.2333   $211.23   $211.25   $211.20  
  Purchase #3 $159.54   10.669%   $176.5613   $176.56   $176.55   $176.60  
  Purchase #4 $69.84   6.793%   $74.5842   $74.58   $74.60   $74.60  
  Purchase #5 $164.89   7.846%   $177.8273   $177.83   $177.85   $177.80  
  Purchase #6 $26.84   3.354%   $27.7402   $27.74   $27.75   $27.70  
  Purchase #7 $147.68   5.873%   $156.3532   $156.35   $156.35   $156.40  
  7 purchase totals = $787.53       $853.4854   $853.48   $853.55   $853.50