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 $66.51   3.121%   $68.5858   $68.59   $68.60   $68.60  
  Purchase #2 $233.28   4.383%   $243.5047   $243.50   $243.50   $243.50  
  Purchase #3 $141.69   8.586%   $153.8555   $153.86   $153.85   $153.90  
  Purchase #4 $72.66   5.622%   $76.7449   $76.74   $76.75   $76.70  
  Purchase #5 $99.92   4.714%   $104.6302   $104.63   $104.65   $104.60  
  Purchase #6 $248.36   3.795%   $257.7853   $257.79   $257.80   $257.80  
  Purchase #7 $234.69   7.250%   $251.705   $251.71   $251.70   $251.70  
  7 purchase totals = $1,097.11       $1,156.8114   $1,156.82   $1,156.85   $1,156.80