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 $212.54   11.668%   $237.3392   $237.34   $237.35   $237.30  
  Purchase #2 $32.37   5.776%   $34.2397   $34.24   $34.25   $34.20  
  Purchase #3 $106.71   5.494%   $112.5726   $112.57   $112.55   $112.60  
  Purchase #4 $132.57   9.196%   $144.7611   $144.76   $144.75   $144.80  
  Purchase #5 $64.50   5.315%   $67.9282   $67.93   $67.95   $67.90  
  Purchase #6 $133.87   3.741%   $138.8781   $138.88   $138.90   $138.90  
  Purchase #7 $100.52   13.417%   $114.0068   $114.01   $114.00   $114.00  
  7 purchase totals = $783.08       $849.7257   $849.73   $849.75   $849.70