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 $44.53   6.723%   $47.5238   $47.52   $47.50   $47.50  
  Purchase #2 $150.48   8.283%   $162.9443   $162.94   $162.95   $162.90  
  Purchase #3 $90.91   12.835%   $102.5783   $102.58   $102.60   $102.60  
  Purchase #4 $22.91   6.558%   $24.4124   $24.41   $24.40   $24.40  
  Purchase #5 $156.39   5.232%   $164.5723   $164.57   $164.55   $164.60  
  Purchase #6 $142.71   3.616%   $147.8704   $147.87   $147.85   $147.90  
  Purchase #7 $208.55   4.421%   $217.77   $217.77   $217.75   $217.80  
  7 purchase totals = $816.48       $867.6715   $867.66   $867.60   $867.70