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 $68.54   9.156%   $74.8155   $74.82   $74.80   $74.80  
  Purchase #2 $246.94   9.163%   $269.5671   $269.57   $269.55   $269.60  
  Purchase #3 $86.29   7.750%   $92.9775   $92.98   $93.00   $93.00  
  Purchase #4 $9.53   12.184%   $10.6911   $10.69   $10.70   $10.70  
  Purchase #5 $90.94   4.855%   $95.3551   $95.36   $95.35   $95.40  
  Purchase #6 $205.65   8.217%   $222.5483   $222.55   $222.55   $222.50  
  Purchase #7 $220.59   13.358%   $250.0564   $250.06   $250.05   $250.10  
  7 purchase totals = $928.48       $1,016.0110   $1,016.03   $1,016.00   $1,016.10