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 $86.57   11.847%   $96.8259   $96.83   $96.85   $96.80  
  Purchase #2 $44.91   12.126%   $50.3558   $50.36   $50.35   $50.40  
  Purchase #3 $94.83   7.612%   $102.0485   $102.05   $102.05   $102.00  
  Purchase #4 $51.40   6.508%   $54.7451   $54.75   $54.75   $54.70  
  Purchase #5 $14.58   3.842%   $15.1402   $15.14   $15.15   $15.10  
  Purchase #6 $86.79   11.621%   $96.8759   $96.88   $96.90   $96.90  
  Purchase #7 $61.91   7.839%   $66.7631   $66.76   $66.75   $66.80  
  7 purchase totals = $440.99       $482.7545   $482.77   $482.80   $482.70