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 $62.41   12.723%   $70.3504   $70.35   $70.35   $70.40  
  Purchase #2 $239.51   3.788%   $248.5826   $248.58   $248.60   $248.60  
  Purchase #3 $231.84   6.339%   $246.5363   $246.54   $246.55   $246.50  
  Purchase #4 $67.82   9.218%   $74.0716   $74.07   $74.05   $74.10  
  Purchase #5 $184.66   11.377%   $205.6688   $205.67   $205.65   $205.70  
  Purchase #6 $150.77   12.362%   $169.4082   $169.41   $169.40   $169.40  
  Purchase #7 $92.96   4.517%   $97.159   $97.16   $97.15   $97.20  
  7 purchase totals = $1,029.97       $1,111.7769   $1,111.78   $1,111.75   $1,111.90