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 $54.83   10.554%   $60.6168   $60.62   $60.60   $60.60  
  Purchase #2 $219.90   13.631%   $249.8746   $249.87   $249.85   $249.90  
  Purchase #3 $186.66   4.286%   $194.6602   $194.66   $194.65   $194.70  
  Purchase #4 $95.55   3.438%   $98.835   $98.84   $98.85   $98.80  
  Purchase #5 $181.85   4.537%   $190.1005   $190.10   $190.10   $190.10  
  Purchase #6 $12.57   8.751%   $13.67   $13.67   $13.65   $13.70  
  Purchase #7 $49.70   3.288%   $51.3341   $51.33   $51.35   $51.30  
  7 purchase totals = $801.06       $859.0912   $859.09   $859.05   $859.10