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 $174.29   11.860%   $194.9608   $194.96   $194.95   $195.00  
  Purchase #2 $242.95   3.493%   $251.4362   $251.44   $251.45   $251.40  
  Purchase #3 $72.45   9.870%   $79.6008   $79.60   $79.60   $79.60  
  Purchase #4 $114.78   8.393%   $124.4135   $124.41   $124.40   $124.40  
  Purchase #5 $235.98   7.151%   $252.8549   $252.85   $252.85   $252.90  
  Purchase #6 $181.49   8.528%   $196.9675   $196.97   $196.95   $197.00  
  Purchase #7 $36.30   4.837%   $38.0558   $38.06   $38.05   $38.10  
  7 purchase totals = $1,058.24       $1,138.2895   $1,138.29   $1,138.25   $1,138.40