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 $49.41   13.581%   $56.1204   $56.12   $56.10   $56.10  
  Purchase #2 $143.87   4.463%   $150.2909   $150.29   $150.30   $150.30  
  Purchase #3 $118.45   5.506%   $124.9719   $124.97   $124.95   $125.00  
  Purchase #4 $61.72   6.158%   $65.5207   $65.52   $65.50   $65.50  
  Purchase #5 $119.88   7.871%   $129.3158   $129.32   $129.30   $129.30  
  Purchase #6 $11.79   8.104%   $12.7455   $12.75   $12.75   $12.70  
  Purchase #7 $200.27   3.202%   $206.6826   $206.68   $206.70   $206.70  
  7 purchase totals = $705.39       $745.6478   $745.65   $745.60   $745.60