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 $221.92   6.815%   $237.0438   $237.04   $237.05   $237.00  
  Purchase #2 $101.82   11.268%   $113.2931   $113.29   $113.30   $113.30  
  Purchase #3 $59.37   6.122%   $63.0046   $63.00   $63.00   $63.00  
  Purchase #4 $36.84   5.555%   $38.8865   $38.89   $38.90   $38.90  
  Purchase #5 $105.87   3.440%   $109.5119   $109.51   $109.50   $109.50  
  Purchase #6 $195.84   13.183%   $221.6576   $221.66   $221.65   $221.70  
  Purchase #7 $169.98   9.497%   $186.123   $186.12   $186.10   $186.10  
  7 purchase totals = $891.64       $969.5205   $969.51   $969.50   $969.50