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 $184.86   7.724%   $199.1386   $199.14   $199.15   $199.10  
  Purchase #2 $30.97   11.382%   $34.495   $34.50   $34.50   $34.50  
  Purchase #3 $26.52   13.209%   $30.023   $30.02   $30.00   $30.00  
  Purchase #4 $198.82   9.709%   $218.1234   $218.12   $218.10   $218.10  
  Purchase #5 $151.94   8.568%   $164.9582   $164.96   $164.95   $165.00  
  Purchase #6 $140.52   3.759%   $145.8021   $145.80   $145.80   $145.80  
  Purchase #7 $219.45   5.174%   $230.8043   $230.80   $230.80   $230.80  
  7 purchase totals = $953.08       $1,023.3446   $1,023.34   $1,023.30   $1,023.30