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 $65.26   13.314%   $73.9487   $73.95   $73.95   $73.90  
  Purchase #2 $14.33   6.102%   $15.2044   $15.20   $15.20   $15.20  
  Purchase #3 $184.67   6.230%   $196.1749   $196.17   $196.15   $196.20  
  Purchase #4 $196.48   8.293%   $212.7741   $212.77   $212.75   $212.80  
  Purchase #5 $130.33   4.777%   $136.5559   $136.56   $136.55   $136.60  
  Purchase #6 $158.79   12.844%   $179.185   $179.19   $179.20   $179.20  
  Purchase #7 $92.47   3.872%   $96.0504   $96.05   $96.05   $96.10  
  7 purchase totals = $842.33       $909.8934   $909.89   $909.85   $910.00