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 $82.63   13.497%   $93.7826   $93.78   $93.80   $93.80  
  Purchase #2 $158.66   8.390%   $171.9716   $171.97   $171.95   $172.00  
  Purchase #3 $150.98   12.155%   $169.3316   $169.33   $169.35   $169.30  
  Purchase #4 $106.81   7.756%   $115.0942   $115.09   $115.10   $115.10  
  Purchase #5 $218.67   12.201%   $245.3499   $245.35   $245.35   $245.30  
  Purchase #6 $162.27   3.232%   $167.5146   $167.51   $167.50   $167.50  
  Purchase #7 $63.34   4.404%   $66.1295   $66.13   $66.15   $66.10  
  7 purchase totals = $943.36       $1,029.1740   $1,029.16   $1,029.20   $1,029.10