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 $241.52   11.441%   $269.1523   $269.15   $269.15   $269.20  
  Purchase #2 $7.48   6.653%   $7.9776   $7.98   $8.00   $8.00  
  Purchase #3 $168.40   8.445%   $182.6214   $182.62   $182.60   $182.60  
  Purchase #4 $117.30   5.308%   $123.5263   $123.53   $123.55   $123.50  
  Purchase #5 $162.27   3.478%   $167.9138   $167.91   $167.90   $167.90  
  Purchase #6 $99.69   3.316%   $102.9957   $103.00   $103.00   $103.00  
  Purchase #7 $248.84   5.627%   $262.8422   $262.84   $262.85   $262.80  
  7 purchase totals = $1,045.50       $1,117.0293   $1,117.03   $1,117.05   $1,117.00