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 $97.57   12.169%   $109.4433   $109.44   $109.45   $109.40  
  Purchase #2 $104.55   4.528%   $109.284   $109.28   $109.30   $109.30  
  Purchase #3 $186.55   12.184%   $209.2793   $209.28   $209.30   $209.30  
  Purchase #4 $171.36   12.272%   $192.3893   $192.39   $192.40   $192.40  
  Purchase #5 $188.27   12.590%   $211.9732   $211.97   $211.95   $212.00  
  Purchase #6 $15.57   10.668%   $17.231   $17.23   $17.25   $17.20  
  Purchase #7 $221.81   11.435%   $247.174   $247.17   $247.15   $247.20  
  7 purchase totals = $985.68       $1,096.7741   $1,096.76   $1,096.80   $1,096.80