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 $114.63   7.448%   $123.1676   $123.17   $123.15   $123.20  
  Purchase #2 $100.82   13.474%   $114.4045   $114.40   $114.40   $114.40  
  Purchase #3 $33.52   9.783%   $36.7993   $36.80   $36.80   $36.80  
  Purchase #4 $201.90   13.765%   $229.6915   $229.69   $229.70   $229.70  
  Purchase #5 $231.89   11.355%   $258.2211   $258.22   $258.20   $258.20  
  Purchase #6 $189.81   8.747%   $206.4127   $206.41   $206.40   $206.40  
  Purchase #7 $59.40   7.742%   $63.9987   $64.00   $64.00   $64.00  
  7 purchase totals = $931.97       $1,032.6954   $1,032.69   $1,032.65   $1,032.70