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 $51.59   10.301%   $56.9043   $56.90   $56.90   $56.90  
  Purchase #2 $232.36   5.798%   $245.8322   $245.83   $245.85   $245.80  
  Purchase #3 $88.70   12.526%   $99.8106   $99.81   $99.80   $99.80  
  Purchase #4 $98.37   4.732%   $103.0249   $103.02   $103.00   $103.00  
  Purchase #5 $167.68   4.827%   $175.7739   $175.77   $175.75   $175.80  
  Purchase #6 $230.51   13.727%   $262.1521   $262.15   $262.15   $262.20  
  Purchase #7 $170.75   5.521%   $180.1771   $180.18   $180.20   $180.20  
  7 purchase totals = $1,039.96       $1,123.6751   $1,123.66   $1,123.65   $1,123.70