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 $134.33   4.540%   $140.4286   $140.43   $140.45   $140.40  
  Purchase #2 $142.90   3.714%   $148.2073   $148.21   $148.20   $148.20  
  Purchase #3 $117.59   3.334%   $121.5105   $121.51   $121.50   $121.50  
  Purchase #4 $75.88   8.322%   $82.1947   $82.19   $82.20   $82.20  
  Purchase #5 $159.72   13.646%   $181.5154   $181.52   $181.50   $181.50  
  Purchase #6 $58.96   8.133%   $63.7552   $63.76   $63.75   $63.80  
  Purchase #7 $30.83   9.177%   $33.6593   $33.66   $33.65   $33.70  
  7 purchase totals = $720.21       $771.2710   $771.28   $771.25   $771.30