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 $30.89   11.464%   $34.4312   $34.43   $34.45   $34.40  
  Purchase #2 $176.76   3.251%   $182.5065   $182.51   $182.50   $182.50  
  Purchase #3 $167.44   11.560%   $186.7961   $186.80   $186.80   $186.80  
  Purchase #4 $238.60   3.321%   $246.5239   $246.52   $246.50   $246.50  
  Purchase #5 $95.82   3.236%   $98.9207   $98.92   $98.90   $98.90  
  Purchase #6 $108.59   4.514%   $113.4918   $113.49   $113.50   $113.50  
  Purchase #7 $142.28   4.245%   $148.3198   $148.32   $148.30   $148.30  
  7 purchase totals = $960.38       $1,010.9900   $1,010.99   $1,010.95   $1,010.90