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 $62.41   9.681%   $68.4519   $68.45   $68.45   $68.50  
  Purchase #2 $5.60   12.525%   $6.3014   $6.30   $6.30   $6.30  
  Purchase #3 $47.80   10.119%   $52.6369   $52.64   $52.65   $52.60  
  Purchase #4 $37.92   8.631%   $41.1929   $41.19   $41.20   $41.20  
  Purchase #5 $221.39   8.707%   $240.6664   $240.67   $240.65   $240.70  
  Purchase #6 $238.86   4.703%   $250.0936   $250.09   $250.10   $250.10  
  Purchase #7 $107.73   11.588%   $120.2138   $120.21   $120.20   $120.20  
  7 purchase totals = $721.71       $779.5569   $779.55   $779.55   $779.60