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 $125.43   7.213%   $134.4773   $134.48   $134.50   $134.50  
  Purchase #2 $241.37   13.514%   $273.9887   $273.99   $274.00   $274.00  
  Purchase #3 $181.91   3.687%   $188.617   $188.62   $188.60   $188.60  
  Purchase #4 $71.91   11.537%   $80.2063   $80.21   $80.20   $80.20  
  Purchase #5 $168.79   4.526%   $176.4294   $176.43   $176.45   $176.40  
  Purchase #6 $16.94   13.594%   $19.2428   $19.24   $19.25   $19.20  
  Purchase #7 $150.38   5.808%   $159.1141   $159.11   $159.10   $159.10  
  7 purchase totals = $956.73       $1,032.0756   $1,032.08   $1,032.10   $1,032.00