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 $176.25   7.154%   $188.8589   $188.86   $188.85   $188.90  
  Purchase #2 $166.46   13.494%   $188.9221   $188.92   $188.90   $188.90  
  Purchase #3 $198.42   5.366%   $209.0672   $209.07   $209.05   $209.10  
  Purchase #4 $57.67   8.608%   $62.6342   $62.63   $62.65   $62.60  
  Purchase #5 $128.59   10.782%   $142.4546   $142.45   $142.45   $142.50  
  Purchase #6 $187.33   6.444%   $199.4015   $199.40   $199.40   $199.40  
  Purchase #7 $211.58   9.638%   $231.9721   $231.97   $231.95   $232.00  
  7 purchase totals = $1,126.30       $1,223.3106   $1,223.30   $1,223.25   $1,223.40