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 $241.81   12.180%   $271.2625   $271.26   $271.25   $271.30  
  Purchase #2 $157.34   6.189%   $167.0778   $167.08   $167.10   $167.10  
  Purchase #3 $179.66   4.208%   $187.2201   $187.22   $187.20   $187.20  
  Purchase #4 $63.53   13.217%   $71.9268   $71.93   $71.95   $71.90  
  Purchase #5 $169.48   13.837%   $192.9309   $192.93   $192.95   $192.90  
  Purchase #6 $145.44   5.633%   $153.6326   $153.63   $153.65   $153.60  
  Purchase #7 $138.72   8.596%   $150.6444   $150.64   $150.65   $150.60  
  7 purchase totals = $1,095.98       $1,194.6951   $1,194.69   $1,194.75   $1,194.60