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 $88.64   8.865%   $96.4979   $96.50   $96.50   $96.50  
  Purchase #2 $127.42   3.226%   $131.5306   $131.53   $131.55   $131.50  
  Purchase #3 $72.42   3.684%   $75.088   $75.09   $75.10   $75.10  
  Purchase #4 $139.45   6.848%   $148.9995   $149.00   $149.00   $149.00  
  Purchase #5 $106.78   5.133%   $112.261   $112.26   $112.25   $112.30  
  Purchase #6 $95.31   3.113%   $98.277   $98.28   $98.30   $98.30  
  Purchase #7 $73.92   8.118%   $79.9208   $79.92   $79.90   $79.90  
  7 purchase totals = $703.94       $742.5748   $742.58   $742.60   $742.60