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 $223.49   12.285%   $250.9457   $250.95   $250.95   $250.90  
  Purchase #2 $163.25   6.159%   $173.3046   $173.30   $173.30   $173.30  
  Purchase #3 $184.25   7.379%   $197.8458   $197.85   $197.85   $197.80  
  Purchase #4 $201.92   11.212%   $224.5593   $224.56   $224.55   $224.60  
  Purchase #5 $55.49   12.632%   $62.4995   $62.50   $62.50   $62.50  
  Purchase #6 $61.67   8.158%   $66.701   $66.70   $66.70   $66.70  
  Purchase #7 $146.81   3.175%   $151.4712   $151.47   $151.45   $151.50  
  7 purchase totals = $1,036.88       $1,127.3271   $1,127.33   $1,127.30   $1,127.30