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 $61.67   9.614%   $67.599   $67.60   $67.60   $67.60  
  Purchase #2 $11.83   11.109%   $13.1442   $13.14   $13.15   $13.10  
  Purchase #3 $145.80   7.391%   $156.5761   $156.58   $156.60   $156.60  
  Purchase #4 $84.50   7.828%   $91.1147   $91.11   $91.10   $91.10  
  Purchase #5 $21.51   8.639%   $23.3682   $23.37   $23.35   $23.40  
  Purchase #6 $220.62   10.833%   $244.5198   $244.52   $244.50   $244.50  
  Purchase #7 $165.87   8.445%   $179.8777   $179.88   $179.90   $179.90  
  7 purchase totals = $711.80       $776.1997   $776.20   $776.20   $776.20