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 $141.79   13.548%   $160.9997   $161.00   $161.00   $161.00  
  Purchase #2 $46.80   3.181%   $48.2887   $48.29   $48.30   $48.30  
  Purchase #3 $62.53   6.660%   $66.6945   $66.69   $66.70   $66.70  
  Purchase #4 $100.79   7.774%   $108.6254   $108.63   $108.65   $108.60  
  Purchase #5 $54.66   13.397%   $61.9828   $61.98   $62.00   $62.00  
  Purchase #6 $113.94   10.341%   $125.7225   $125.72   $125.70   $125.70  
  Purchase #7 $216.85   7.236%   $232.5413   $232.54   $232.55   $232.50  
  7 purchase totals = $737.36       $804.8549   $804.85   $804.90   $804.80