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 $59.49   3.859%   $61.7857   $61.79   $61.80   $61.80  
  Purchase #2 $227.29   9.398%   $248.6507   $248.65   $248.65   $248.70  
  Purchase #3 $241.90   3.652%   $250.7342   $250.73   $250.75   $250.70  
  Purchase #4 $143.99   3.665%   $149.2672   $149.27   $149.25   $149.30  
  Purchase #5 $229.61   9.837%   $252.1967   $252.20   $252.20   $252.20  
  Purchase #6 $6.97   13.842%   $7.9348   $7.93   $7.95   $7.90  
  Purchase #7 $228.68   11.440%   $254.841   $254.84   $254.85   $254.80  
  7 purchase totals = $1,137.93       $1,225.4103   $1,225.41   $1,225.45   $1,225.40