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 $203.92   10.517%   $225.3663   $225.37   $225.35   $225.40  
  Purchase #2 $226.64   10.266%   $249.9069   $249.91   $249.90   $249.90  
  Purchase #3 $54.84   6.245%   $58.2648   $58.26   $58.25   $58.30  
  Purchase #4 $121.77   7.514%   $130.9198   $130.92   $130.90   $130.90  
  Purchase #5 $176.72   3.623%   $183.1226   $183.12   $183.10   $183.10  
  Purchase #6 $52.83   3.551%   $54.706   $54.71   $54.70   $54.70  
  Purchase #7 $43.61   4.353%   $45.5083   $45.51   $45.50   $45.50  
  7 purchase totals = $880.33       $947.7947   $947.80   $947.70   $947.80