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 $40.88   6.484%   $43.5307   $43.53   $43.55   $43.50  
  Purchase #2 $171.64   13.619%   $195.0157   $195.02   $195.00   $195.00  
  Purchase #3 $52.57   10.539%   $58.1104   $58.11   $58.10   $58.10  
  Purchase #4 $243.28   5.832%   $257.4681   $257.47   $257.45   $257.50  
  Purchase #5 $12.71   7.444%   $13.6561   $13.66   $13.65   $13.70  
  Purchase #6 $57.83   5.606%   $61.0719   $61.07   $61.05   $61.10  
  Purchase #7 $192.84   11.186%   $214.4111   $214.41   $214.40   $214.40  
  7 purchase totals = $771.75       $843.2640   $843.27   $843.20   $843.30