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 $60.59   11.324%   $67.4512   $67.45   $67.45   $67.50  
  Purchase #2 $203.46   3.163%   $209.8954   $209.90   $209.90   $209.90  
  Purchase #3 $171.54   5.570%   $181.0948   $181.09   $181.10   $181.10  
  Purchase #4 $25.38   4.723%   $26.5787   $26.58   $26.60   $26.60  
  Purchase #5 $248.58   9.666%   $272.6077   $272.61   $272.60   $272.60  
  Purchase #6 $122.92   5.870%   $130.1354   $130.14   $130.15   $130.10  
  Purchase #7 $142.53   11.812%   $159.3656   $159.37   $159.35   $159.40  
  7 purchase totals = $975.00       $1,047.1288   $1,047.14   $1,047.15   $1,047.20