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 $216.57   13.618%   $246.0625   $246.06   $246.05   $246.10  
  Purchase #2 $231.76   7.250%   $248.5626   $248.56   $248.55   $248.60  
  Purchase #3 $113.47   3.800%   $117.7819   $117.78   $117.80   $117.80  
  Purchase #4 $25.92   10.236%   $28.5732   $28.57   $28.55   $28.60  
  Purchase #5 $57.28   11.611%   $63.9308   $63.93   $63.95   $63.90  
  Purchase #6 $83.32   6.313%   $88.58   $88.58   $88.60   $88.60  
  Purchase #7 $240.75   4.803%   $252.3132   $252.31   $252.30   $252.30  
  7 purchase totals = $969.07       $1,045.8042   $1,045.79   $1,045.80   $1,045.90