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 $101.36   10.345%   $111.8457   $111.85   $111.85   $111.80  
  Purchase #2 $209.37   9.613%   $229.4967   $229.50   $229.50   $229.50  
  Purchase #3 $195.87   13.275%   $221.8717   $221.87   $221.85   $221.90  
  Purchase #4 $200.69   12.651%   $226.0793   $226.08   $226.10   $226.10  
  Purchase #5 $41.67   11.834%   $46.6012   $46.60   $46.60   $46.60  
  Purchase #6 $142.53   7.261%   $152.8791   $152.88   $152.90   $152.90  
  Purchase #7 $60.43   8.827%   $65.7642   $65.76   $65.75   $65.80  
  7 purchase totals = $951.92       $1,054.5379   $1,054.54   $1,054.55   $1,054.60