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 $126.53   10.651%   $140.0067   $140.01   $140.00   $140.00  
  Purchase #2 $205.48   9.787%   $225.5903   $225.59   $225.60   $225.60  
  Purchase #3 $67.26   8.605%   $73.0477   $73.05   $73.05   $73.00  
  Purchase #4 $231.80   6.619%   $247.1428   $247.14   $247.15   $247.10  
  Purchase #5 $187.64   3.339%   $193.9053   $193.91   $193.90   $193.90  
  Purchase #6 $140.52   9.155%   $153.3846   $153.38   $153.40   $153.40  
  Purchase #7 $99.81   3.492%   $103.2954   $103.30   $103.30   $103.30  
  7 purchase totals = $1,059.04       $1,136.3728   $1,136.38   $1,136.40   $1,136.30