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 $218.63   7.318%   $234.6293   $234.63   $234.65   $234.60  
  Purchase #2 $199.92   3.374%   $206.6653   $206.67   $206.65   $206.70  
  Purchase #3 $111.94   8.172%   $121.0877   $121.09   $121.10   $121.10  
  Purchase #4 $212.60   8.419%   $230.4988   $230.50   $230.50   $230.50  
  Purchase #5 $186.26   10.422%   $205.672   $205.67   $205.65   $205.70  
  Purchase #6 $145.66   8.830%   $158.5218   $158.52   $158.50   $158.50  
  Purchase #7 $37.93   12.466%   $42.6584   $42.66   $42.65   $42.70  
  7 purchase totals = $1,112.94       $1,199.7333   $1,199.74   $1,199.70   $1,199.80