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 $250.45   10.585%   $276.9601   $276.96   $276.95   $277.00  
  Purchase #2 $96.43   8.253%   $104.3884   $104.39   $104.40   $104.40  
  Purchase #3 $111.39   10.728%   $123.3399   $123.34   $123.35   $123.30  
  Purchase #4 $167.27   3.478%   $173.0877   $173.09   $173.10   $173.10  
  Purchase #5 $239.39   8.703%   $260.2241   $260.22   $260.20   $260.20  
  Purchase #6 $49.68   10.814%   $55.0524   $55.05   $55.05   $55.10  
  Purchase #7 $202.39   10.301%   $223.2382   $223.24   $223.25   $223.20  
  7 purchase totals = $1,117.00       $1,216.2908   $1,216.29   $1,216.30   $1,216.30