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 $183.35   9.649%   $201.0414   $201.04   $201.05   $201.00  
  Purchase #2 $153.28   5.395%   $161.5495   $161.55   $161.55   $161.50  
  Purchase #3 $110.29   6.640%   $117.6133   $117.61   $117.60   $117.60  
  Purchase #4 $195.65   5.159%   $205.7436   $205.74   $205.75   $205.70  
  Purchase #5 $17.73   4.345%   $18.5004   $18.50   $18.50   $18.50  
  Purchase #6 $102.76   4.545%   $107.4304   $107.43   $107.45   $107.40  
  Purchase #7 $137.70   7.340%   $147.8072   $147.81   $147.80   $147.80  
  7 purchase totals = $900.76       $959.6858   $959.68   $959.70   $959.50