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 $219.69   12.219%   $246.5339   $246.53   $246.55   $246.50  
  Purchase #2 $90.83   7.622%   $97.7531   $97.75   $97.75   $97.80  
  Purchase #3 $220.90   8.263%   $239.153   $239.15   $239.15   $239.20  
  Purchase #4 $184.36   5.264%   $194.0647   $194.06   $194.05   $194.10  
  Purchase #5 $123.84   10.170%   $136.4345   $136.43   $136.45   $136.40  
  Purchase #6 $173.47   4.692%   $181.6092   $181.61   $181.60   $181.60  
  Purchase #7 $30.97   5.530%   $32.6826   $32.68   $32.70   $32.70  
  7 purchase totals = $1,044.06       $1,128.2310   $1,128.21   $1,128.25   $1,128.30