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 $182.76   10.485%   $201.9224   $201.92   $201.90   $201.90  
  Purchase #2 $53.55   7.581%   $57.6096   $57.61   $57.60   $57.60  
  Purchase #3 $204.66   7.679%   $220.3758   $220.38   $220.40   $220.40  
  Purchase #4 $119.82   12.675%   $135.0072   $135.01   $135.00   $135.00  
  Purchase #5 $80.30   13.440%   $91.0923   $91.09   $91.10   $91.10  
  Purchase #6 $149.54   8.853%   $162.7788   $162.78   $162.80   $162.80  
  Purchase #7 $55.91   10.363%   $61.704   $61.70   $61.70   $61.70  
  7 purchase totals = $846.54       $930.4901   $930.49   $930.50   $930.50