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 $45.76   7.182%   $49.0465   $49.05   $49.05   $49.00  
  Purchase #2 $86.32   13.257%   $97.7634   $97.76   $97.75   $97.80  
  Purchase #3 $162.38   7.867%   $175.1544   $175.15   $175.15   $175.20  
  Purchase #4 $232.97   11.156%   $258.9601   $258.96   $258.95   $259.00  
  Purchase #5 $163.61   3.294%   $168.9993   $169.00   $169.00   $169.00  
  Purchase #6 $41.88   4.115%   $43.6034   $43.60   $43.60   $43.60  
  Purchase #7 $133.49   13.160%   $151.0573   $151.06   $151.05   $151.10  
  7 purchase totals = $866.41       $944.5844   $944.58   $944.55   $944.70