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 $31.57   9.672%   $34.6235   $34.62   $34.60   $34.60  
  Purchase #2 $228.42   5.104%   $240.0786   $240.08   $240.10   $240.10  
  Purchase #3 $207.25   5.599%   $218.8539   $218.85   $218.85   $218.90  
  Purchase #4 $50.42   9.578%   $55.2492   $55.25   $55.25   $55.20  
  Purchase #5 $206.68   13.696%   $234.9869   $234.99   $235.00   $235.00  
  Purchase #6 $33.64   11.868%   $37.6324   $37.63   $37.65   $37.60  
  Purchase #7 $35.56   3.506%   $36.8067   $36.81   $36.80   $36.80  
  7 purchase totals = $793.54       $858.2312   $858.23   $858.25   $858.20