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 $53.45   11.683%   $59.6946   $59.69   $59.70   $59.70  
  Purchase #2 $244.65   6.245%   $259.9284   $259.93   $259.95   $259.90  
  Purchase #3 $81.79   6.856%   $87.3975   $87.40   $87.40   $87.40  
  Purchase #4 $70.92   9.382%   $77.5737   $77.57   $77.55   $77.60  
  Purchase #5 $216.32   12.611%   $243.6001   $243.60   $243.60   $243.60  
  Purchase #6 $65.44   4.260%   $68.2277   $68.23   $68.25   $68.20  
  Purchase #7 $57.73   9.362%   $63.1347   $63.13   $63.15   $63.10  
  7 purchase totals = $790.30       $859.5567   $859.55   $859.60   $859.50