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 $116.76   10.653%   $129.1984   $129.20   $129.20   $129.20  
  Purchase #2 $142.61   8.504%   $154.7376   $154.74   $154.75   $154.70  
  Purchase #3 $11.45   11.124%   $12.7237   $12.72   $12.70   $12.70  
  Purchase #4 $205.74   3.781%   $213.519   $213.52   $213.50   $213.50  
  Purchase #5 $234.59   13.555%   $266.3887   $266.39   $266.40   $266.40  
  Purchase #6 $217.50   12.145%   $243.9154   $243.92   $243.90   $243.90  
  Purchase #7 $172.25   4.454%   $179.922   $179.92   $179.90   $179.90  
  7 purchase totals = $1,100.90       $1,200.4048   $1,200.41   $1,200.35   $1,200.30