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 $68.99   7.387%   $74.0863   $74.09   $74.10   $74.10  
  Purchase #2 $68.89   6.347%   $73.2624   $73.26   $73.25   $73.30  
  Purchase #3 $243.33   12.538%   $273.8387   $273.84   $273.85   $273.80  
  Purchase #4 $87.54   7.688%   $94.2701   $94.27   $94.25   $94.30  
  Purchase #5 $71.76   5.659%   $75.8209   $75.82   $75.80   $75.80  
  Purchase #6 $161.47   3.165%   $166.5805   $166.58   $166.60   $166.60  
  Purchase #7 $181.84   8.805%   $197.851   $197.85   $197.85   $197.90  
  7 purchase totals = $883.82       $955.7099   $955.71   $955.70   $955.80