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 $173.77   7.183%   $186.2519   $186.25   $186.25   $186.30  
  Purchase #2 $92.33   6.503%   $98.3342   $98.33   $98.35   $98.30  
  Purchase #3 $199.96   3.727%   $207.4125   $207.41   $207.40   $207.40  
  Purchase #4 $136.54   7.712%   $147.07   $147.07   $147.05   $147.10  
  Purchase #5 $148.88   3.171%   $153.601   $153.60   $153.60   $153.60  
  Purchase #6 $190.93   4.125%   $198.8059   $198.81   $198.80   $198.80  
  Purchase #7 $219.99   7.226%   $235.8865   $235.89   $235.90   $235.90  
  7 purchase totals = $1,162.40       $1,227.3620   $1,227.36   $1,227.35   $1,227.40