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 $204.93   12.487%   $230.5196   $230.52   $230.50   $230.50  
  Purchase #2 $136.90   8.546%   $148.5995   $148.60   $148.60   $148.60  
  Purchase #3 $132.93   9.409%   $145.4374   $145.44   $145.45   $145.40  
  Purchase #4 $102.67   4.461%   $107.2501   $107.25   $107.25   $107.30  
  Purchase #5 $17.69   11.659%   $19.7525   $19.75   $19.75   $19.80  
  Purchase #6 $119.63   5.469%   $126.1726   $126.17   $126.15   $126.20  
  Purchase #7 $222.28   11.636%   $248.1445   $248.14   $248.15   $248.10  
  7 purchase totals = $937.03       $1,025.8762   $1,025.87   $1,025.85   $1,025.90