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 $184.59   10.515%   $203.9996   $204.00   $204.00   $204.00  
  Purchase #2 $248.47   5.658%   $262.5284   $262.53   $262.55   $262.50  
  Purchase #3 $151.25   10.106%   $166.5353   $166.54   $166.55   $166.50  
  Purchase #4 $245.79   8.680%   $267.1246   $267.12   $267.10   $267.10  
  Purchase #5 $22.54   11.249%   $25.0755   $25.08   $25.10   $25.10  
  Purchase #6 $8.83   11.810%   $9.8728   $9.87   $9.85   $9.90  
  Purchase #7 $63.57   10.749%   $70.4031   $70.40   $70.40   $70.40  
  7 purchase totals = $925.04       $1,005.5393   $1,005.54   $1,005.55   $1,005.50