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 $237.64   11.766%   $265.6007   $265.60   $265.60   $265.60  
  Purchase #2 $184.78   8.751%   $200.9501   $200.95   $200.95   $201.00  
  Purchase #3 $238.57   7.632%   $256.7777   $256.78   $256.80   $256.80  
  Purchase #4 $156.89   13.407%   $177.9242   $177.92   $177.90   $177.90  
  Purchase #5 $148.79   4.183%   $155.0139   $155.01   $155.00   $155.00  
  Purchase #6 $69.50   6.573%   $74.0682   $74.07   $74.05   $74.10  
  Purchase #7 $76.61   12.301%   $86.0338   $86.03   $86.05   $86.00  
  7 purchase totals = $1,112.78       $1,216.3686   $1,216.36   $1,216.35   $1,216.40