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 $186.72   9.142%   $203.7899   $203.79   $203.80   $203.80  
  Purchase #2 $128.79   10.509%   $142.3245   $142.32   $142.30   $142.30  
  Purchase #3 $97.79   8.825%   $106.42   $106.42   $106.40   $106.40  
  Purchase #4 $201.45   4.367%   $210.2473   $210.25   $210.25   $210.20  
  Purchase #5 $182.34   11.428%   $203.1778   $203.18   $203.20   $203.20  
  Purchase #6 $41.89   6.746%   $44.7159   $44.72   $44.70   $44.70  
  Purchase #7 $12.93   8.246%   $13.9962   $14.00   $14.00   $14.00  
  7 purchase totals = $851.91       $924.6716   $924.68   $924.65   $924.60