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 $158.27   11.646%   $176.7021   $176.70   $176.70   $176.70  
  Purchase #2 $113.64   9.122%   $124.0062   $124.01   $124.00   $124.00  
  Purchase #3 $111.34   13.554%   $126.431   $126.43   $126.45   $126.40  
  Purchase #4 $240.63   12.350%   $270.3478   $270.35   $270.35   $270.30  
  Purchase #5 $166.79   5.384%   $175.77   $175.77   $175.75   $175.80  
  Purchase #6 $73.38   5.272%   $77.2486   $77.25   $77.25   $77.20  
  Purchase #7 $236.69   6.763%   $252.6973   $252.70   $252.70   $252.70  
  7 purchase totals = $1,100.74       $1,203.2030   $1,203.21   $1,203.20   $1,203.10