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 $237.44   3.597%   $245.9807   $245.98   $246.00   $246.00  
  Purchase #2 $84.57   6.806%   $90.3258   $90.33   $90.35   $90.30  
  Purchase #3 $24.30   13.272%   $27.5251   $27.53   $27.55   $27.50  
  Purchase #4 $214.83   11.682%   $239.9264   $239.93   $239.95   $239.90  
  Purchase #5 $136.40   5.503%   $143.9061   $143.91   $143.90   $143.90  
  Purchase #6 $184.60   9.692%   $202.4914   $202.49   $202.50   $202.50  
  Purchase #7 $86.34   5.508%   $91.0956   $91.10   $91.10   $91.10  
  7 purchase totals = $968.48       $1,041.2511   $1,041.27   $1,041.35   $1,041.20