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 $65.81   5.831%   $69.6474   $69.65   $69.65   $69.60  
  Purchase #2 $38.34   13.414%   $43.4829   $43.48   $43.50   $43.50  
  Purchase #3 $238.90   4.191%   $248.9123   $248.91   $248.90   $248.90  
  Purchase #4 $66.82   8.429%   $72.4523   $72.45   $72.45   $72.50  
  Purchase #5 $120.36   11.840%   $134.6106   $134.61   $134.60   $134.60  
  Purchase #6 $119.96   8.180%   $129.7727   $129.77   $129.75   $129.80  
  Purchase #7 $219.61   3.111%   $226.4421   $226.44   $226.45   $226.40  
  7 purchase totals = $869.80       $925.3203   $925.31   $925.30   $925.30