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 $50.33   4.477%   $52.5833   $52.58   $52.60   $52.60  
  Purchase #2 $11.40   10.759%   $12.6265   $12.63   $12.65   $12.60  
  Purchase #3 $145.72   8.295%   $157.8075   $157.81   $157.80   $157.80  
  Purchase #4 $201.38   5.581%   $212.619   $212.62   $212.60   $212.60  
  Purchase #5 $174.36   9.467%   $190.8667   $190.87   $190.85   $190.90  
  Purchase #6 $187.35   8.678%   $203.6082   $203.61   $203.60   $203.60  
  Purchase #7 $233.58   9.617%   $256.0434   $256.04   $256.05   $256.00  
  7 purchase totals = $1,004.12       $1,086.1546   $1,086.16   $1,086.15   $1,086.10