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 $141.95   8.180%   $153.5615   $153.56   $153.55   $153.60  
  Purchase #2 $214.50   10.181%   $236.3382   $236.34   $236.35   $236.30  
  Purchase #3 $213.47   6.127%   $226.5493   $226.55   $226.55   $226.50  
  Purchase #4 $66.40   11.396%   $73.9669   $73.97   $73.95   $74.00  
  Purchase #5 $163.99   4.683%   $171.6697   $171.67   $171.65   $171.70  
  Purchase #6 $39.66   6.738%   $42.3323   $42.33   $42.35   $42.30  
  Purchase #7 $135.26   12.806%   $152.5814   $152.58   $152.60   $152.60  
  7 purchase totals = $975.23       $1,056.9993   $1,057.00   $1,057.00   $1,057.00