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 $61.97   12.151%   $69.5   $69.50   $69.50   $69.50  
  Purchase #2 $134.99   13.729%   $153.5228   $153.52   $153.50   $153.50  
  Purchase #3 $111.62   13.365%   $126.538   $126.54   $126.55   $126.50  
  Purchase #4 $213.46   5.114%   $224.3763   $224.38   $224.40   $224.40  
  Purchase #5 $90.30   10.364%   $99.6587   $99.66   $99.65   $99.70  
  Purchase #6 $170.82   3.769%   $177.2582   $177.26   $177.25   $177.30  
  Purchase #7 $246.87   7.513%   $265.4173   $265.42   $265.40   $265.40  
  7 purchase totals = $1,030.03       $1,116.2713   $1,116.28   $1,116.25   $1,116.30