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 $35.32   3.355%   $36.505   $36.51   $36.50   $36.50  
  Purchase #2 $109.40   3.636%   $113.3778   $113.38   $113.40   $113.40  
  Purchase #3 $83.27   8.246%   $90.1364   $90.14   $90.15   $90.10  
  Purchase #4 $245.99   3.296%   $254.0978   $254.10   $254.10   $254.10  
  Purchase #5 $126.49   9.619%   $138.6571   $138.66   $138.65   $138.70  
  Purchase #6 $194.70   4.431%   $203.3272   $203.33   $203.35   $203.30  
  Purchase #7 $85.41   3.255%   $88.1901   $88.19   $88.20   $88.20  
  7 purchase totals = $880.58       $924.2914   $924.31   $924.35   $924.30