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 $238.63   8.577%   $259.0973   $259.10   $259.10   $259.10  
  Purchase #2 $240.86   4.554%   $251.8288   $251.83   $251.85   $251.80  
  Purchase #3 $59.73   10.847%   $66.2089   $66.21   $66.20   $66.20  
  Purchase #4 $242.26   7.326%   $260.008   $260.01   $260.00   $260.00  
  Purchase #5 $145.51   11.180%   $161.778   $161.78   $161.80   $161.80  
  Purchase #6 $161.78   3.305%   $167.1268   $167.13   $167.15   $167.10  
  Purchase #7 $221.32   7.692%   $238.3439   $238.34   $238.35   $238.30  
  7 purchase totals = $1,310.09       $1,404.3917   $1,404.40   $1,404.45   $1,404.30