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 $241.61   11.548%   $269.5111   $269.51   $269.50   $269.50  
  Purchase #2 $50.62   12.333%   $56.863   $56.86   $56.85   $56.90  
  Purchase #3 $178.52   10.784%   $197.7716   $197.77   $197.75   $197.80  
  Purchase #4 $62.84   5.702%   $66.4231   $66.42   $66.40   $66.40  
  Purchase #5 $181.32   7.836%   $195.5282   $195.53   $195.55   $195.50  
  Purchase #6 $216.41   11.257%   $240.7713   $240.77   $240.75   $240.80  
  Purchase #7 $249.66   10.294%   $275.36   $275.36   $275.35   $275.40  
  7 purchase totals = $1,180.98       $1,302.2283   $1,302.22   $1,302.15   $1,302.30