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 $240.82   13.257%   $272.7455   $272.75   $272.75   $272.70  
  Purchase #2 $212.84   10.269%   $234.6965   $234.70   $234.70   $234.70  
  Purchase #3 $168.87   11.378%   $188.084   $188.08   $188.10   $188.10  
  Purchase #4 $195.75   12.791%   $220.7884   $220.79   $220.80   $220.80  
  Purchase #5 $248.43   11.734%   $277.5808   $277.58   $277.60   $277.60  
  Purchase #6 $112.50   7.722%   $121.1873   $121.19   $121.20   $121.20  
  Purchase #7 $145.38   3.863%   $150.996   $151.00   $151.00   $151.00  
  7 purchase totals = $1,324.59       $1,466.0785   $1,466.09   $1,466.15   $1,466.10