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 $219.51   6.157%   $233.0252   $233.03   $233.05   $233.00  
  Purchase #2 $221.97   10.804%   $245.9516   $245.95   $245.95   $246.00  
  Purchase #3 $99.55   12.177%   $111.6722   $111.67   $111.65   $111.70  
  Purchase #4 $11.52   3.610%   $11.9359   $11.94   $11.95   $11.90  
  Purchase #5 $187.37   4.766%   $196.3001   $196.30   $196.30   $196.30  
  Purchase #6 $158.86   7.132%   $170.1899   $170.19   $170.20   $170.20  
  Purchase #7 $115.26   12.409%   $129.5626   $129.56   $129.55   $129.60  
  7 purchase totals = $1,014.04       $1,098.6375   $1,098.64   $1,098.65   $1,098.70