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 $224.30   5.197%   $235.9569   $235.96   $235.95   $236.00  
  Purchase #2 $246.59   6.640%   $262.9636   $262.96   $262.95   $263.00  
  Purchase #3 $13.55   7.667%   $14.5889   $14.59   $14.60   $14.60  
  Purchase #4 $29.31   5.233%   $30.8438   $30.84   $30.85   $30.80  
  Purchase #5 $144.76   5.413%   $152.5959   $152.60   $152.60   $152.60  
  Purchase #6 $191.86   9.233%   $209.5744   $209.57   $209.55   $209.60  
  Purchase #7 $90.94   3.324%   $93.9628   $93.96   $93.95   $94.00  
  7 purchase totals = $941.31       $1,000.4863   $1,000.48   $1,000.45   $1,000.60