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 $205.64   13.283%   $232.9552   $232.96   $232.95   $233.00  
  Purchase #2 $152.84   7.315%   $164.0202   $164.02   $164.00   $164.00  
  Purchase #3 $152.99   8.633%   $166.1976   $166.20   $166.20   $166.20  
  Purchase #4 $203.88   3.800%   $211.6274   $211.63   $211.65   $211.60  
  Purchase #5 $35.90   13.804%   $40.8556   $40.86   $40.85   $40.90  
  Purchase #6 $237.34   9.212%   $259.2038   $259.20   $259.20   $259.20  
  Purchase #7 $118.42   3.822%   $122.946   $122.95   $122.95   $122.90  
  7 purchase totals = $1,107.01       $1,197.8058   $1,197.82   $1,197.80   $1,197.80