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 $106.91   11.821%   $119.5478   $119.55   $119.55   $119.50  
  Purchase #2 $183.71   9.399%   $200.9769   $200.98   $201.00   $201.00  
  Purchase #3 $80.53   13.534%   $91.4289   $91.43   $91.45   $91.40  
  Purchase #4 $51.39   13.724%   $58.4428   $58.44   $58.45   $58.40  
  Purchase #5 $146.74   10.828%   $162.629   $162.63   $162.65   $162.60  
  Purchase #6 $130.61   8.570%   $141.8033   $141.80   $141.80   $141.80  
  Purchase #7 $54.84   8.268%   $59.3742   $59.37   $59.35   $59.40  
  7 purchase totals = $754.73       $834.2029   $834.20   $834.25   $834.10