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 $201.91   11.124%   $224.3705   $224.37   $224.35   $224.40  
  Purchase #2 $53.29   4.216%   $55.5367   $55.54   $55.55   $55.50  
  Purchase #3 $162.49   10.496%   $179.545   $179.55   $179.55   $179.50  
  Purchase #4 $227.82   4.294%   $237.6026   $237.60   $237.60   $237.60  
  Purchase #5 $223.86   7.811%   $241.3457   $241.35   $241.35   $241.30  
  Purchase #6 $213.86   6.195%   $227.1086   $227.11   $227.10   $227.10  
  Purchase #7 $156.42   4.764%   $163.8718   $163.87   $163.85   $163.90  
  7 purchase totals = $1,239.65       $1,329.3809   $1,329.39   $1,329.35   $1,329.30