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 $226.75   9.772%   $248.908   $248.91   $248.90   $248.90  
  Purchase #2 $245.33   9.616%   $268.9209   $268.92   $268.90   $268.90  
  Purchase #3 $202.86   13.365%   $229.9722   $229.97   $229.95   $230.00  
  Purchase #4 $86.32   7.661%   $92.933   $92.93   $92.95   $92.90  
  Purchase #5 $154.70   13.723%   $175.9295   $175.93   $175.95   $175.90  
  Purchase #6 $133.51   3.751%   $138.518   $138.52   $138.50   $138.50  
  Purchase #7 $179.47   12.596%   $202.076   $202.08   $202.10   $202.10  
  7 purchase totals = $1,228.94       $1,357.2576   $1,357.26   $1,357.25   $1,357.20