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 $156.93   5.337%   $165.3054   $165.31   $165.30   $165.30  
  Purchase #2 $215.93   4.179%   $224.9537   $224.95   $224.95   $225.00  
  Purchase #3 $103.91   13.169%   $117.5939   $117.59   $117.60   $117.60  
  Purchase #4 $221.95   8.225%   $240.2054   $240.21   $240.20   $240.20  
  Purchase #5 $216.40   8.745%   $235.3242   $235.32   $235.30   $235.30  
  Purchase #6 $209.33   5.316%   $220.458   $220.46   $220.45   $220.50  
  Purchase #7 $25.56   7.237%   $27.4098   $27.41   $27.40   $27.40  
  7 purchase totals = $1,150.01       $1,231.2504   $1,231.25   $1,231.20   $1,231.30