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 $244.96   6.831%   $261.6932   $261.69   $261.70   $261.70  
  Purchase #2 $137.46   5.686%   $145.276   $145.28   $145.30   $145.30  
  Purchase #3 $240.95   13.451%   $273.3602   $273.36   $273.35   $273.40  
  Purchase #4 $14.66   11.483%   $16.3434   $16.34   $16.35   $16.30  
  Purchase #5 $203.27   6.347%   $216.1715   $216.17   $216.15   $216.20  
  Purchase #6 $44.45   13.695%   $50.5374   $50.54   $50.55   $50.50  
  Purchase #7 $193.55   12.757%   $218.2412   $218.24   $218.25   $218.20  
  7 purchase totals = $1,079.30       $1,181.6229   $1,181.62   $1,181.65   $1,181.60