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 $57.59   6.533%   $61.3524   $61.35   $61.35   $61.40  
  Purchase #2 $42.38   8.600%   $46.0247   $46.02   $46.00   $46.00  
  Purchase #3 $208.66   8.587%   $226.5776   $226.58   $226.60   $226.60  
  Purchase #4 $212.26   10.349%   $234.2268   $234.23   $234.25   $234.20  
  Purchase #5 $120.34   6.173%   $127.7686   $127.77   $127.75   $127.80  
  Purchase #6 $136.70   5.474%   $144.183   $144.18   $144.20   $144.20  
  Purchase #7 $163.81   12.760%   $184.7122   $184.71   $184.70   $184.70  
  7 purchase totals = $941.74       $1,024.8453   $1,024.84   $1,024.85   $1,024.90