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 $246.40   5.249%   $259.3335   $259.33   $259.35   $259.30  
  Purchase #2 $88.99   8.433%   $96.4945   $96.49   $96.50   $96.50  
  Purchase #3 $92.99   9.843%   $102.143   $102.14   $102.15   $102.10  
  Purchase #4 $183.61   3.793%   $190.5743   $190.57   $190.55   $190.60  
  Purchase #5 $86.81   6.702%   $92.628   $92.63   $92.65   $92.60  
  Purchase #6 $237.63   5.386%   $250.4288   $250.43   $250.45   $250.40  
  Purchase #7 $39.95   11.714%   $44.6297   $44.63   $44.65   $44.60  
  7 purchase totals = $976.38       $1,036.2318   $1,036.22   $1,036.30   $1,036.10