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 $246.50   5.330%   $259.6385   $259.64   $259.65   $259.60  
  Purchase #2 $180.55   5.572%   $190.6102   $190.61   $190.60   $190.60  
  Purchase #3 $6.36   5.546%   $6.7127   $6.71   $6.70   $6.70  
  Purchase #4 $81.62   7.521%   $87.7586   $87.76   $87.75   $87.80  
  Purchase #5 $150.29   7.160%   $161.0508   $161.05   $161.05   $161.10  
  Purchase #6 $173.36   6.866%   $185.2629   $185.26   $185.25   $185.30  
  Purchase #7 $172.93   11.328%   $192.5195   $192.52   $192.50   $192.50  
  7 purchase totals = $1,011.61       $1,083.5532   $1,083.55   $1,083.50   $1,083.60