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 $161.80   13.326%   $183.3615   $183.36   $183.35   $183.40  
  Purchase #2 $153.92   6.847%   $164.4589   $164.46   $164.45   $164.50  
  Purchase #3 $27.27   11.772%   $30.4802   $30.48   $30.50   $30.50  
  Purchase #4 $218.49   8.864%   $237.857   $237.86   $237.85   $237.90  
  Purchase #5 $217.72   12.727%   $245.4292   $245.43   $245.45   $245.40  
  Purchase #6 $156.78   11.671%   $175.0778   $175.08   $175.10   $175.10  
  Purchase #7 $59.38   12.669%   $66.9029   $66.90   $66.90   $66.90  
  7 purchase totals = $995.36       $1,103.5675   $1,103.57   $1,103.60   $1,103.70