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 $77.45   5.823%   $81.9599   $81.96   $81.95   $82.00  
  Purchase #2 $152.58   4.621%   $159.6307   $159.63   $159.65   $159.60  
  Purchase #3 $33.92   8.355%   $36.754   $36.75   $36.75   $36.80  
  Purchase #4 $147.55   13.577%   $167.5829   $167.58   $167.60   $167.60  
  Purchase #5 $140.49   4.633%   $146.9989   $147.00   $147.00   $147.00  
  Purchase #6 $211.81   5.541%   $223.5464   $223.55   $223.55   $223.50  
  Purchase #7 $33.36   9.556%   $36.5479   $36.55   $36.55   $36.50  
  7 purchase totals = $797.16       $853.0207   $853.02   $853.05   $853.00