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 $89.28   10.419%   $98.5821   $98.58   $98.60   $98.60  
  Purchase #2 $250.41   11.152%   $278.3357   $278.34   $278.35   $278.30  
  Purchase #3 $112.56   13.427%   $127.6734   $127.67   $127.65   $127.70  
  Purchase #4 $109.64   8.416%   $118.8673   $118.87   $118.85   $118.90  
  Purchase #5 $194.97   12.552%   $219.4426   $219.44   $219.45   $219.40  
  Purchase #6 $242.61   11.461%   $270.4155   $270.42   $270.40   $270.40  
  Purchase #7 $108.47   13.419%   $123.0256   $123.03   $123.05   $123.00  
  7 purchase totals = $1,107.94       $1,236.3422   $1,236.35   $1,236.35   $1,236.30