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 $25.29   5.751%   $26.7444   $26.74   $26.75   $26.70  
  Purchase #2 $177.28   4.104%   $184.5556   $184.56   $184.55   $184.60  
  Purchase #3 $193.72   12.746%   $218.4116   $218.41   $218.40   $218.40  
  Purchase #4 $117.46   8.146%   $127.0283   $127.03   $127.05   $127.00  
  Purchase #5 $175.67   5.154%   $184.724   $184.72   $184.70   $184.70  
  Purchase #6 $156.53   4.165%   $163.0495   $163.05   $163.05   $163.00  
  Purchase #7 $148.94   3.748%   $154.5223   $154.52   $154.50   $154.50  
  7 purchase totals = $994.89       $1,059.0357   $1,059.03   $1,059.00   $1,058.90