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 $185.51   11.572%   $206.9772   $206.98   $207.00   $207.00  
  Purchase #2 $47.94   5.245%   $50.4545   $50.45   $50.45   $50.50  
  Purchase #3 $38.99   3.502%   $40.3554   $40.36   $40.35   $40.40  
  Purchase #4 $120.51   6.160%   $127.9334   $127.93   $127.95   $127.90  
  Purchase #5 $243.56   3.492%   $252.0651   $252.07   $252.05   $252.10  
  Purchase #6 $233.65   12.336%   $262.4731   $262.47   $262.45   $262.50  
  Purchase #7 $116.68   5.141%   $122.6785   $122.68   $122.70   $122.70  
  7 purchase totals = $986.84       $1,062.9372   $1,062.94   $1,062.95   $1,063.10