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 $85.76   12.173%   $96.1996   $96.20   $96.20   $96.20  
  Purchase #2 $150.54   5.265%   $158.4659   $158.47   $158.45   $158.50  
  Purchase #3 $227.38   8.769%   $247.319   $247.32   $247.30   $247.30  
  Purchase #4 $156.95   8.440%   $170.1966   $170.20   $170.20   $170.20  
  Purchase #5 $101.79   7.630%   $109.5566   $109.56   $109.55   $109.60  
  Purchase #6 $56.70   12.867%   $63.9956   $64.00   $64.00   $64.00  
  Purchase #7 $85.55   4.662%   $89.5383   $89.54   $89.55   $89.50  
  7 purchase totals = $864.67       $935.2716   $935.29   $935.25   $935.30