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 $119.88   12.280%   $134.6013   $134.60   $134.60   $134.60  
  Purchase #2 $169.25   11.615%   $188.9084   $188.91   $188.90   $188.90  
  Purchase #3 $39.69   11.235%   $44.1492   $44.15   $44.15   $44.10  
  Purchase #4 $97.67   9.209%   $106.6644   $106.66   $106.65   $106.70  
  Purchase #5 $137.72   12.398%   $154.7945   $154.79   $154.80   $154.80  
  Purchase #6 $131.92   11.296%   $146.8217   $146.82   $146.80   $146.80  
  Purchase #7 $228.63   3.291%   $236.1542   $236.15   $236.15   $236.20  
  7 purchase totals = $924.76       $1,012.0937   $1,012.08   $1,012.05   $1,012.10