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 $88.73   9.104%   $96.808   $96.81   $96.80   $96.80  
  Purchase #2 $236.39   6.775%   $252.4054   $252.41   $252.40   $252.40  
  Purchase #3 $218.55   8.858%   $237.9092   $237.91   $237.90   $237.90  
  Purchase #4 $177.32   6.174%   $188.2677   $188.27   $188.25   $188.30  
  Purchase #5 $232.45   6.386%   $247.2943   $247.29   $247.30   $247.30  
  Purchase #6 $5.68   10.640%   $6.2844   $6.28   $6.30   $6.30  
  Purchase #7 $55.86   10.347%   $61.6398   $61.64   $61.65   $61.60  
  7 purchase totals = $1,014.98       $1,090.6088   $1,090.61   $1,090.60   $1,090.60