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 $54.67   11.785%   $61.1129   $61.11   $61.10   $61.10  
  Purchase #2 $225.50   10.531%   $249.2474   $249.25   $249.25   $249.20  
  Purchase #3 $114.74   11.249%   $127.6471   $127.65   $127.65   $127.60  
  Purchase #4 $76.98   4.613%   $80.5311   $80.53   $80.55   $80.50  
  Purchase #5 $63.52   9.856%   $69.7805   $69.78   $69.80   $69.80  
  Purchase #6 $211.27   10.700%   $233.8759   $233.88   $233.90   $233.90  
  Purchase #7 $182.96   13.318%   $207.3266   $207.33   $207.35   $207.30  
  7 purchase totals = $929.64       $1,029.5215   $1,029.53   $1,029.60   $1,029.40