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 $102.44   13.237%   $116   $116.00   $116.00   $116.00  
  Purchase #2 $206.71   6.275%   $219.6811   $219.68   $219.70   $219.70  
  Purchase #3 $21.54   12.705%   $24.2767   $24.28   $24.30   $24.30  
  Purchase #4 $186.76   9.240%   $204.0166   $204.02   $204.00   $204.00  
  Purchase #5 $30.58   3.729%   $31.7203   $31.72   $31.70   $31.70  
  Purchase #6 $235.37   13.671%   $267.5474   $267.55   $267.55   $267.50  
  Purchase #7 $79.97   5.170%   $84.1044   $84.10   $84.10   $84.10  
  7 purchase totals = $863.37       $947.3465   $947.35   $947.35   $947.30