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 $112.84   9.571%   $123.6399   $123.64   $123.65   $123.60  
  Purchase #2 $114.88   5.292%   $120.9594   $120.96   $120.95   $121.00  
  Purchase #3 $230.67   3.423%   $238.5658   $238.57   $238.55   $238.60  
  Purchase #4 $32.32   11.551%   $36.0533   $36.05   $36.05   $36.10  
  Purchase #5 $73.57   5.136%   $77.3486   $77.35   $77.35   $77.30  
  Purchase #6 $167.83   11.254%   $186.7176   $186.72   $186.70   $186.70  
  Purchase #7 $248.65   12.762%   $280.3827   $280.38   $280.40   $280.40  
  7 purchase totals = $980.76       $1,063.6673   $1,063.67   $1,063.65   $1,063.70