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 $46.64   13.581%   $52.9742   $52.97   $52.95   $53.00  
  Purchase #2 $207.49   4.346%   $216.5075   $216.51   $216.50   $216.50  
  Purchase #3 $51.65   10.639%   $57.145   $57.15   $57.15   $57.10  
  Purchase #4 $90.91   8.802%   $98.9119   $98.91   $98.90   $98.90  
  Purchase #5 $223.90   12.811%   $252.5838   $252.58   $252.60   $252.60  
  Purchase #6 $58.31   8.738%   $63.4051   $63.41   $63.40   $63.40  
  Purchase #7 $190.34   7.813%   $205.2113   $205.21   $205.20   $205.20  
  7 purchase totals = $869.24       $946.7388   $946.74   $946.70   $946.70