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 $52.93   13.200%   $59.9168   $59.92   $59.90   $59.90  
  Purchase #2 $216.85   10.670%   $239.9879   $239.99   $240.00   $240.00  
  Purchase #3 $49.30   13.644%   $56.0265   $56.03   $56.05   $56.00  
  Purchase #4 $159.82   11.772%   $178.634   $178.63   $178.65   $178.60  
  Purchase #5 $135.45   6.378%   $144.089   $144.09   $144.10   $144.10  
  Purchase #6 $242.67   4.213%   $252.8937   $252.89   $252.90   $252.90  
  Purchase #7 $190.99   10.650%   $211.3304   $211.33   $211.35   $211.30  
  7 purchase totals = $1,048.01       $1,142.8783   $1,142.88   $1,142.95   $1,142.80