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 $53.57   8.343%   $58.0393   $58.04   $58.05   $58.00  
  Purchase #2 $11.70   13.740%   $13.3076   $13.31   $13.30   $13.30  
  Purchase #3 $115.27   8.242%   $124.7706   $124.77   $124.75   $124.80  
  Purchase #4 $174.57   9.479%   $191.1175   $191.12   $191.10   $191.10  
  Purchase #5 $71.94   7.594%   $77.4031   $77.40   $77.40   $77.40  
  Purchase #6 $242.56   11.255%   $269.8601   $269.86   $269.85   $269.90  
  Purchase #7 $62.93   11.657%   $70.2658   $70.27   $70.25   $70.30  
  7 purchase totals = $732.54       $804.7640   $804.77   $804.70   $804.80