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 $222.76   11.266%   $247.8561   $247.86   $247.85   $247.90  
  Purchase #2 $61.49   11.599%   $68.6222   $68.62   $68.60   $68.60  
  Purchase #3 $226.61   6.453%   $241.2331   $241.23   $241.25   $241.20  
  Purchase #4 $162.88   12.279%   $182.88   $182.88   $182.90   $182.90  
  Purchase #5 $51.81   9.327%   $56.6423   $56.64   $56.65   $56.60  
  Purchase #6 $147.43   12.651%   $166.0814   $166.08   $166.10   $166.10  
  Purchase #7 $126.94   11.402%   $141.4137   $141.41   $141.40   $141.40  
  7 purchase totals = $999.92       $1,104.7288   $1,104.72   $1,104.75   $1,104.70