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 $246.95   8.470%   $267.8667   $267.87   $267.85   $267.90  
  Purchase #2 $63.27   4.157%   $65.9001   $65.90   $65.90   $65.90  
  Purchase #3 $102.53   9.163%   $111.9248   $111.92   $111.90   $111.90  
  Purchase #4 $224.65   9.613%   $246.2456   $246.25   $246.25   $246.20  
  Purchase #5 $23.30   3.791%   $24.1833   $24.18   $24.20   $24.20  
  Purchase #6 $227.38   5.393%   $239.6426   $239.64   $239.65   $239.60  
  Purchase #7 $177.83   7.588%   $191.3237   $191.32   $191.30   $191.30  
  7 purchase totals = $1,065.91       $1,147.0868   $1,147.08   $1,147.05   $1,147.00