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 $188.33   3.592%   $195.0948   $195.09   $195.10   $195.10  
  Purchase #2 $136.73   8.123%   $147.8366   $147.84   $147.85   $147.80  
  Purchase #3 $197.34   8.809%   $214.7237   $214.72   $214.70   $214.70  
  Purchase #4 $248.71   3.732%   $257.9919   $257.99   $258.00   $258.00  
  Purchase #5 $247.81   7.811%   $267.1664   $267.17   $267.15   $267.20  
  Purchase #6 $148.27   9.282%   $162.0324   $162.03   $162.05   $162.00  
  Purchase #7 $248.84   13.336%   $282.0253   $282.03   $282.05   $282.00  
  7 purchase totals = $1,416.03       $1,526.8711   $1,526.87   $1,526.90   $1,526.80