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 $163.61   13.371%   $185.4863   $185.49   $185.50   $185.50  
  Purchase #2 $128.69   3.103%   $132.6833   $132.68   $132.70   $132.70  
  Purchase #3 $210.29   7.466%   $225.9903   $225.99   $226.00   $226.00  
  Purchase #4 $226.36   12.678%   $255.0579   $255.06   $255.05   $255.10  
  Purchase #5 $90.70   3.114%   $93.5244   $93.52   $93.50   $93.50  
  Purchase #6 $184.76   11.732%   $206.436   $206.44   $206.45   $206.40  
  Purchase #7 $20.99   10.604%   $23.2158   $23.22   $23.20   $23.20  
  7 purchase totals = $1,025.40       $1,122.3940   $1,122.40   $1,122.40   $1,122.40