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 $181.87   11.506%   $202.796   $202.80   $202.80   $202.80  
  Purchase #2 $89.27   10.483%   $98.6282   $98.63   $98.65   $98.60  
  Purchase #3 $229.74   12.336%   $258.0807   $258.08   $258.10   $258.10  
  Purchase #4 $51.65   8.530%   $56.0557   $56.06   $56.05   $56.10  
  Purchase #5 $206.55   10.522%   $228.2832   $228.28   $228.30   $228.30  
  Purchase #6 $163.81   11.436%   $182.5433   $182.54   $182.55   $182.50  
  Purchase #7 $143.97   11.245%   $160.1594   $160.16   $160.15   $160.20  
  7 purchase totals = $1,066.86       $1,186.5465   $1,186.55   $1,186.60   $1,186.60