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 $66.65   4.227%   $69.4673   $69.47   $69.45   $69.50  
  Purchase #2 $43.33   3.186%   $44.7105   $44.71   $44.70   $44.70  
  Purchase #3 $169.52   3.470%   $175.4023   $175.40   $175.40   $175.40  
  Purchase #4 $38.91   9.775%   $42.7135   $42.71   $42.70   $42.70  
  Purchase #5 $194.42   7.424%   $208.8537   $208.85   $208.85   $208.90  
  Purchase #6 $248.77   9.304%   $271.9156   $271.92   $271.90   $271.90  
  Purchase #7 $36.61   8.396%   $39.6838   $39.68   $39.70   $39.70  
  7 purchase totals = $798.21       $852.7467   $852.74   $852.70   $852.80