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 $86.25   11.158%   $95.8738   $95.87   $95.85   $95.90  
  Purchase #2 $48.72   8.434%   $52.829   $52.83   $52.85   $52.80  
  Purchase #3 $117.30   7.483%   $126.0776   $126.08   $126.10   $126.10  
  Purchase #4 $135.93   12.649%   $153.1238   $153.12   $153.10   $153.10  
  Purchase #5 $156.30   6.126%   $165.8749   $165.87   $165.85   $165.90  
  Purchase #6 $120.68   13.533%   $137.0116   $137.01   $137.00   $137.00  
  Purchase #7 $115.61   6.371%   $122.9755   $122.98   $123.00   $123.00  
  7 purchase totals = $780.79       $853.7662   $853.76   $853.75   $853.80