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 $54.86   11.615%   $61.232   $61.23   $61.25   $61.20  
  Purchase #2 $170.51   3.794%   $176.9791   $176.98   $177.00   $177.00  
  Purchase #3 $137.69   7.254%   $147.678   $147.68   $147.70   $147.70  
  Purchase #4 $229.27   9.747%   $251.6169   $251.62   $251.60   $251.60  
  Purchase #5 $228.46   12.464%   $256.9353   $256.94   $256.95   $256.90  
  Purchase #6 $71.88   6.636%   $76.65   $76.65   $76.65   $76.70  
  Purchase #7 $223.38   7.520%   $240.1782   $240.18   $240.20   $240.20  
  7 purchase totals = $1,116.05       $1,211.2695   $1,211.28   $1,211.35   $1,211.30