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 $222.99   13.654%   $253.4371   $253.44   $253.45   $253.40  
  Purchase #2 $77.31   13.303%   $87.5945   $87.59   $87.60   $87.60  
  Purchase #3 $176.31   9.596%   $193.2287   $193.23   $193.25   $193.20  
  Purchase #4 $45.93   8.795%   $49.9695   $49.97   $49.95   $50.00  
  Purchase #5 $102.88   4.150%   $107.1495   $107.15   $107.15   $107.10  
  Purchase #6 $155.58   8.271%   $168.448   $168.45   $168.45   $168.40  
  Purchase #7 $163.33   10.763%   $180.9092   $180.91   $180.90   $180.90  
  7 purchase totals = $944.33       $1,040.7365   $1,040.74   $1,040.75   $1,040.60