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 $113.71   8.348%   $123.2025   $123.20   $123.20   $123.20  
  Purchase #2 $232.96   11.184%   $259.0142   $259.01   $259.00   $259.00  
  Purchase #3 $171.27   10.319%   $188.9434   $188.94   $188.95   $188.90  
  Purchase #4 $185.89   4.258%   $193.8052   $193.81   $193.80   $193.80  
  Purchase #5 $62.41   13.481%   $70.8235   $70.82   $70.80   $70.80  
  Purchase #6 $199.27   11.790%   $222.7639   $222.76   $222.75   $222.80  
  Purchase #7 $60.60   10.168%   $66.7618   $66.76   $66.75   $66.80  
  7 purchase totals = $1,026.11       $1,125.3145   $1,125.30   $1,125.25   $1,125.30