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 $227.44   6.253%   $241.6618   $241.66   $241.65   $241.70  
  Purchase #2 $165.33   9.134%   $180.4312   $180.43   $180.45   $180.40  
  Purchase #3 $103.95   13.444%   $117.925   $117.93   $117.95   $117.90  
  Purchase #4 $20.81   7.632%   $22.3982   $22.40   $22.40   $22.40  
  Purchase #5 $197.70   4.605%   $206.8041   $206.80   $206.80   $206.80  
  Purchase #6 $117.41   8.144%   $126.9719   $126.97   $126.95   $127.00  
  Purchase #7 $57.84   5.552%   $61.0513   $61.05   $61.05   $61.10  
  7 purchase totals = $890.48       $957.2435   $957.24   $957.25   $957.30