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 $41.31   6.266%   $43.8985   $43.90   $43.90   $43.90  
  Purchase #2 $163.59   7.372%   $175.6499   $175.65   $175.65   $175.60  
  Purchase #3 $186.77   6.441%   $198.7999   $198.80   $198.80   $198.80  
  Purchase #4 $84.57   13.829%   $96.2652   $96.27   $96.25   $96.30  
  Purchase #5 $9.49   8.131%   $10.2616   $10.26   $10.25   $10.30  
  Purchase #6 $175.97   3.656%   $182.4035   $182.40   $182.40   $182.40  
  Purchase #7 $87.98   6.435%   $93.6415   $93.64   $93.65   $93.60  
  7 purchase totals = $749.68       $800.9201   $800.92   $800.90   $800.90