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 $178.79   8.620%   $194.2017   $194.20   $194.20   $194.20  
  Purchase #2 $137.52   4.649%   $143.9133   $143.91   $143.90   $143.90  
  Purchase #3 $112.36   13.310%   $127.3151   $127.32   $127.30   $127.30  
  Purchase #4 $21.90   11.722%   $24.4671   $24.47   $24.45   $24.50  
  Purchase #5 $180.41   3.288%   $186.3419   $186.34   $186.35   $186.30  
  Purchase #6 $246.87   4.611%   $258.2532   $258.25   $258.25   $258.30  
  Purchase #7 $102.78   6.312%   $109.2675   $109.27   $109.25   $109.30  
  7 purchase totals = $980.63       $1,043.7598   $1,043.76   $1,043.70   $1,043.80