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 $205.53   13.357%   $232.9826   $232.98   $233.00   $233.00  
  Purchase #2 $45.85   13.486%   $52.0333   $52.03   $52.05   $52.00  
  Purchase #3 $106.39   7.234%   $114.0863   $114.09   $114.10   $114.10  
  Purchase #4 $221.87   11.338%   $247.0256   $247.03   $247.05   $247.00  
  Purchase #5 $154.87   4.231%   $161.4225   $161.42   $161.40   $161.40  
  Purchase #6 $220.28   10.225%   $242.8036   $242.80   $242.80   $242.80  
  Purchase #7 $186.36   4.402%   $194.5636   $194.56   $194.55   $194.60  
  7 purchase totals = $1,141.15       $1,244.9175   $1,244.91   $1,244.95   $1,244.90