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 $221.74   5.787%   $234.5721   $234.57   $234.55   $234.60  
  Purchase #2 $43.51   7.277%   $46.6762   $46.68   $46.70   $46.70  
  Purchase #3 $183.96   6.814%   $196.495   $196.50   $196.50   $196.50  
  Purchase #4 $64.81   8.476%   $70.3033   $70.30   $70.30   $70.30  
  Purchase #5 $202.37   6.742%   $216.0138   $216.01   $216.00   $216.00  
  Purchase #6 $127.31   4.628%   $133.2019   $133.20   $133.20   $133.20  
  Purchase #7 $54.43   8.348%   $58.9738   $58.97   $58.95   $59.00  
  7 purchase totals = $898.13       $956.2361   $956.23   $956.20   $956.30