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 $54.75   3.592%   $56.7166   $56.72   $56.70   $56.70  
  Purchase #2 $131.99   11.182%   $146.7491   $146.75   $146.75   $146.70  
  Purchase #3 $240.95   7.431%   $258.855   $258.86   $258.85   $258.90  
  Purchase #4 $12.84   9.367%   $14.0427   $14.04   $14.05   $14.00  
  Purchase #5 $79.51   8.457%   $86.2342   $86.23   $86.25   $86.20  
  Purchase #6 $222.37   9.555%   $243.6175   $243.62   $243.60   $243.60  
  Purchase #7 $246.76   6.753%   $263.4237   $263.42   $263.40   $263.40  
  7 purchase totals = $989.17       $1,069.6388   $1,069.64   $1,069.60   $1,069.50