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 $156.94   13.213%   $177.6765   $177.68   $177.70   $177.70  
  Purchase #2 $152.99   10.727%   $169.4012   $169.40   $169.40   $169.40  
  Purchase #3 $83.92   4.517%   $87.7107   $87.71   $87.70   $87.70  
  Purchase #4 $83.61   3.467%   $86.5088   $86.51   $86.50   $86.50  
  Purchase #5 $202.75   7.192%   $217.3318   $217.33   $217.35   $217.30  
  Purchase #6 $134.54   13.154%   $152.2374   $152.24   $152.25   $152.20  
  Purchase #7 $159.41   8.388%   $172.7813   $172.78   $172.80   $172.80  
  7 purchase totals = $974.16       $1,063.6477   $1,063.65   $1,063.70   $1,063.60