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 $227.28   10.501%   $251.1467   $251.15   $251.15   $251.10  
  Purchase #2 $249.52   10.308%   $275.2405   $275.24   $275.25   $275.20  
  Purchase #3 $57.43   7.173%   $61.5495   $61.55   $61.55   $61.50  
  Purchase #4 $227.59   10.403%   $251.2662   $251.27   $251.25   $251.30  
  Purchase #5 $241.82   9.747%   $265.3902   $265.39   $265.40   $265.40  
  Purchase #6 $181.75   7.129%   $194.707   $194.71   $194.70   $194.70  
  Purchase #7 $54.64   11.486%   $60.916   $60.92   $60.90   $60.90  
  7 purchase totals = $1,240.03       $1,360.2161   $1,360.23   $1,360.20   $1,360.10