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 $151.96   12.581%   $171.0781   $171.08   $171.10   $171.10  
  Purchase #2 $166.91   6.610%   $177.9428   $177.94   $177.95   $177.90  
  Purchase #3 $67.63   10.151%   $74.4951   $74.50   $74.50   $74.50  
  Purchase #4 $102.76   10.819%   $113.8776   $113.88   $113.90   $113.90  
  Purchase #5 $245.61   11.762%   $274.4986   $274.50   $274.50   $274.50  
  Purchase #6 $65.48   3.479%   $67.758   $67.76   $67.75   $67.80  
  Purchase #7 $78.95   4.228%   $82.288   $82.29   $82.30   $82.30  
  7 purchase totals = $879.30       $961.9382   $961.95   $962.00   $962.00