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 $97.55   4.702%   $102.1368   $102.14   $102.15   $102.10  
  Purchase #2 $106.61   11.157%   $118.5045   $118.50   $118.50   $118.50  
  Purchase #3 $80.53   8.616%   $87.4685   $87.47   $87.45   $87.50  
  Purchase #4 $54.53   12.855%   $61.5398   $61.54   $61.55   $61.50  
  Purchase #5 $208.26   12.200%   $233.6677   $233.67   $233.65   $233.70  
  Purchase #6 $246.39   8.184%   $266.5546   $266.55   $266.55   $266.60  
  Purchase #7 $122.90   11.157%   $136.612   $136.61   $136.60   $136.60  
  7 purchase totals = $916.77       $1,006.4839   $1,006.48   $1,006.45   $1,006.50