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 $58.94   5.776%   $62.3444   $62.34   $62.35   $62.30  
  Purchase #2 $131.34   8.184%   $142.0889   $142.09   $142.10   $142.10  
  Purchase #3 $128.79   5.295%   $135.6094   $135.61   $135.60   $135.60  
  Purchase #4 $222.54   6.579%   $237.1809   $237.18   $237.20   $237.20  
  Purchase #5 $36.29   9.493%   $39.735   $39.74   $39.75   $39.70  
  Purchase #6 $120.87   8.730%   $131.422   $131.42   $131.40   $131.40  
  Purchase #7 $228.58   6.156%   $242.6514   $242.65   $242.65   $242.70  
  7 purchase totals = $927.35       $991.0320   $991.03   $991.05   $991.00