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 $105.69   7.446%   $113.5597   $113.56   $113.55   $113.60  
  Purchase #2 $131.64   12.828%   $148.5268   $148.53   $148.55   $148.50  
  Purchase #3 $139.64   11.411%   $155.5743   $155.57   $155.55   $155.60  
  Purchase #4 $125.60   5.167%   $132.0898   $132.09   $132.10   $132.10  
  Purchase #5 $173.79   4.688%   $181.9373   $181.94   $181.95   $181.90  
  Purchase #6 $237.97   10.322%   $262.5333   $262.53   $262.55   $262.50  
  Purchase #7 $234.65   7.528%   $252.3145   $252.31   $252.30   $252.30  
  7 purchase totals = $1,148.98       $1,246.5357   $1,246.53   $1,246.55   $1,246.50