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 $75.49   12.393%   $84.8455   $84.85   $84.85   $84.80  
  Purchase #2 $118.42   3.195%   $122.2035   $122.20   $122.20   $122.20  
  Purchase #3 $176.78   5.379%   $186.289   $186.29   $186.30   $186.30  
  Purchase #4 $176.62   12.545%   $198.777   $198.78   $198.80   $198.80  
  Purchase #5 $145.92   6.538%   $155.4602   $155.46   $155.45   $155.50  
  Purchase #6 $218.37   13.178%   $247.1468   $247.15   $247.15   $247.10  
  Purchase #7 $143.26   5.566%   $151.2339   $151.23   $151.25   $151.20  
  7 purchase totals = $1,054.86       $1,145.9559   $1,145.96   $1,146.00   $1,145.90