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 $236.86   8.155%   $256.1759   $256.18   $256.20   $256.20  
  Purchase #2 $217.64   8.793%   $236.7771   $236.78   $236.80   $236.80  
  Purchase #3 $226.82   4.352%   $236.6912   $236.69   $236.70   $236.70  
  Purchase #4 $35.40   6.836%   $37.8199   $37.82   $37.80   $37.80  
  Purchase #5 $152.61   5.871%   $161.5697   $161.57   $161.55   $161.60  
  Purchase #6 $187.70   5.615%   $198.2394   $198.24   $198.25   $198.20  
  Purchase #7 $124.79   11.637%   $139.3118   $139.31   $139.30   $139.30  
  7 purchase totals = $1,181.82       $1,266.5850   $1,266.59   $1,266.60   $1,266.60