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 $237.97   10.409%   $262.7403   $262.74   $262.75   $262.70  
  Purchase #2 $23.38   3.607%   $24.2233   $24.22   $24.20   $24.20  
  Purchase #3 $105.37   3.364%   $108.9146   $108.91   $108.90   $108.90  
  Purchase #4 $141.62   4.608%   $148.1458   $148.15   $148.15   $148.10  
  Purchase #5 $122.49   13.704%   $139.276   $139.28   $139.30   $139.30  
  Purchase #6 $170.78   11.734%   $190.8193   $190.82   $190.80   $190.80  
  Purchase #7 $91.45   6.542%   $97.4327   $97.43   $97.45   $97.40  
  7 purchase totals = $893.06       $971.5520   $971.55   $971.55   $971.40