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 $139.66   5.424%   $147.2352   $147.24   $147.25   $147.20  
  Purchase #2 $175.64   4.749%   $183.9811   $183.98   $184.00   $184.00  
  Purchase #3 $59.81   7.867%   $64.5153   $64.52   $64.50   $64.50  
  Purchase #4 $208.90   3.818%   $216.8758   $216.88   $216.90   $216.90  
  Purchase #5 $218.37   7.116%   $233.9092   $233.91   $233.90   $233.90  
  Purchase #6 $78.73   10.813%   $87.2431   $87.24   $87.25   $87.20  
  Purchase #7 $237.85   5.399%   $250.6915   $250.69   $250.70   $250.70  
  7 purchase totals = $1,118.96       $1,184.4512   $1,184.46   $1,184.50   $1,184.40