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 $247.41   7.327%   $265.5377   $265.54   $265.55   $265.50  
  Purchase #2 $168.56   9.114%   $183.9226   $183.92   $183.90   $183.90  
  Purchase #3 $177.54   8.264%   $192.2119   $192.21   $192.20   $192.20  
  Purchase #4 $175.89   4.772%   $184.2835   $184.28   $184.30   $184.30  
  Purchase #5 $98.52   3.511%   $101.979   $101.98   $102.00   $102.00  
  Purchase #6 $250.45   8.797%   $272.4821   $272.48   $272.50   $272.50  
  Purchase #7 $205.51   9.112%   $224.2361   $224.24   $224.25   $224.20  
  7 purchase totals = $1,323.88       $1,424.6529   $1,424.65   $1,424.70   $1,424.60