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 $204.97   13.546%   $232.7352   $232.74   $232.75   $232.70  
  Purchase #2 $69.86   6.813%   $74.6196   $74.62   $74.60   $74.60  
  Purchase #3 $104.40   3.255%   $107.7982   $107.80   $107.80   $107.80  
  Purchase #4 $111.70   13.582%   $126.8711   $126.87   $126.85   $126.90  
  Purchase #5 $126.85   5.869%   $134.2948   $134.29   $134.30   $134.30  
  Purchase #6 $127.48   11.832%   $142.5634   $142.56   $142.55   $142.60  
  Purchase #7 $98.65   7.432%   $105.9817   $105.98   $106.00   $106.00  
  7 purchase totals = $843.91       $924.8640   $924.86   $924.85   $924.90