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 $32.86   5.830%   $34.7757   $34.78   $34.80   $34.80  
  Purchase #2 $235.55   12.611%   $265.2552   $265.26   $265.25   $265.30  
  Purchase #3 $202.84   6.327%   $215.6737   $215.67   $215.65   $215.70  
  Purchase #4 $46.30   8.234%   $50.1123   $50.11   $50.10   $50.10  
  Purchase #5 $57.69   4.244%   $60.1384   $60.14   $60.15   $60.10  
  Purchase #6 $105.63   4.726%   $110.6221   $110.62   $110.60   $110.60  
  Purchase #7 $202.87   11.109%   $225.4068   $225.41   $225.40   $225.40  
  7 purchase totals = $883.74       $961.9842   $961.99   $961.95   $962.00