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 $23.47   11.587%   $26.1895   $26.19   $26.20   $26.20  
  Purchase #2 $187.33   8.354%   $202.9795   $202.98   $203.00   $203.00  
  Purchase #3 $181.52   8.194%   $196.3937   $196.39   $196.40   $196.40  
  Purchase #4 $29.69   10.346%   $32.7617   $32.76   $32.75   $32.80  
  Purchase #5 $177.59   5.209%   $186.8407   $186.84   $186.85   $186.80  
  Purchase #6 $142.64   10.299%   $157.3305   $157.33   $157.35   $157.30  
  Purchase #7 $169.26   5.853%   $179.1668   $179.17   $179.15   $179.20  
  7 purchase totals = $911.50       $981.6624   $981.66   $981.70   $981.70