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 $243.77   9.160%   $266.0993   $266.10   $266.10   $266.10  
  Purchase #2 $232.41   11.735%   $259.6833   $259.68   $259.70   $259.70  
  Purchase #3 $108.48   4.310%   $113.1555   $113.16   $113.15   $113.20  
  Purchase #4 $209.84   5.347%   $221.0601   $221.06   $221.05   $221.10  
  Purchase #5 $180.69   6.579%   $192.5776   $192.58   $192.60   $192.60  
  Purchase #6 $44.83   12.291%   $50.3401   $50.34   $50.35   $50.30  
  Purchase #7 $100.86   4.610%   $105.5096   $105.51   $105.50   $105.50  
  7 purchase totals = $1,120.88       $1,208.4255   $1,208.43   $1,208.45   $1,208.50