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 $187.71   7.229%   $201.2796   $201.28   $201.30   $201.30  
  Purchase #2 $130.69   5.351%   $137.6832   $137.68   $137.70   $137.70  
  Purchase #3 $159.96   9.604%   $175.3226   $175.32   $175.30   $175.30  
  Purchase #4 $6.67   13.727%   $7.5856   $7.59   $7.60   $7.60  
  Purchase #5 $177.26   13.724%   $201.5872   $201.59   $201.60   $201.60  
  Purchase #6 $247.43   8.608%   $268.7288   $268.73   $268.75   $268.70  
  Purchase #7 $38.88   12.179%   $43.6152   $43.62   $43.60   $43.60  
  7 purchase totals = $948.60       $1,035.8022   $1,035.81   $1,035.85   $1,035.80