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 $81.32   4.569%   $85.0355   $85.04   $85.05   $85.00  
  Purchase #2 $250.27   4.667%   $261.9501   $261.95   $261.95   $262.00  
  Purchase #3 $234.91   8.527%   $254.9408   $254.94   $254.95   $254.90  
  Purchase #4 $98.34   3.767%   $102.0445   $102.04   $102.05   $102.00  
  Purchase #5 $20.64   6.337%   $21.948   $21.95   $21.95   $21.90  
  Purchase #6 $138.44   4.772%   $145.0464   $145.05   $145.05   $145.00  
  Purchase #7 $217.68   13.311%   $246.6554   $246.66   $246.65   $246.70  
  7 purchase totals = $1,041.60       $1,117.6207   $1,117.63   $1,117.65   $1,117.50