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 $31.30   9.668%   $34.3261   $34.33   $34.35   $34.30  
  Purchase #2 $101.94   11.831%   $114.0005   $114.00   $114.00   $114.00  
  Purchase #3 $188.41   12.471%   $211.9066   $211.91   $211.90   $211.90  
  Purchase #4 $32.61   5.422%   $34.3781   $34.38   $34.40   $34.40  
  Purchase #5 $88.60   13.715%   $100.7515   $100.75   $100.75   $100.80  
  Purchase #6 $167.37   10.319%   $184.6409   $184.64   $184.65   $184.60  
  Purchase #7 $23.71   3.359%   $24.5064   $24.51   $24.50   $24.50  
  7 purchase totals = $633.94       $704.5101   $704.52   $704.55   $704.50