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 $76.48   11.338%   $85.1513   $85.15   $85.15   $85.20  
  Purchase #2 $149.69   9.291%   $163.5977   $163.60   $163.60   $163.60  
  Purchase #3 $156.70   5.467%   $165.2668   $165.27   $165.25   $165.30  
  Purchase #4 $216.26   5.264%   $227.6439   $227.64   $227.65   $227.60  
  Purchase #5 $109.97   12.568%   $123.791   $123.79   $123.80   $123.80  
  Purchase #6 $70.33   7.679%   $75.7306   $75.73   $75.75   $75.70  
  Purchase #7 $196.92   13.662%   $223.8232   $223.82   $223.80   $223.80  
  7 purchase totals = $976.35       $1,065.0045   $1,065.00   $1,065.00   $1,065.00