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 $33.61   6.675%   $35.8535   $35.85   $35.85   $35.90  
  Purchase #2 $223.78   8.589%   $243.0005   $243.00   $243.00   $243.00  
  Purchase #3 $180.58   6.326%   $192.0035   $192.00   $192.00   $192.00  
  Purchase #4 $168.99   11.350%   $188.1704   $188.17   $188.15   $188.20  
  Purchase #5 $233.79   10.795%   $259.0276   $259.03   $259.05   $259.00  
  Purchase #6 $170.26   6.755%   $181.7611   $181.76   $181.75   $181.80  
  Purchase #7 $92.41   8.198%   $99.9858   $99.99   $100.00   $100.00  
  7 purchase totals = $1,103.42       $1,199.8024   $1,199.80   $1,199.80   $1,199.90