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 $119.27   11.522%   $133.0123   $133.01   $133.00   $133.00  
  Purchase #2 $224.25   12.643%   $252.6019   $252.60   $252.60   $252.60  
  Purchase #3 $186.81   13.319%   $211.6912   $211.69   $211.70   $211.70  
  Purchase #4 $42.89   13.248%   $48.5721   $48.57   $48.55   $48.60  
  Purchase #5 $132.48   5.548%   $139.83   $139.83   $139.85   $139.80  
  Purchase #6 $30.40   13.168%   $34.4031   $34.40   $34.40   $34.40  
  Purchase #7 $205.78   9.842%   $226.0329   $226.03   $226.05   $226.00  
  7 purchase totals = $941.88       $1,046.1435   $1,046.13   $1,046.15   $1,046.10