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 $147.53   10.162%   $162.522   $162.52   $162.50   $162.50  
  Purchase #2 $13.38   12.482%   $15.0501   $15.05   $15.05   $15.10  
  Purchase #3 $204.60   8.394%   $221.7741   $221.77   $221.75   $221.80  
  Purchase #4 $241.41   13.874%   $274.9032   $274.90   $274.90   $274.90  
  Purchase #5 $181.39   12.837%   $204.675   $204.68   $204.70   $204.70  
  Purchase #6 $20.96   12.659%   $23.6133   $23.61   $23.60   $23.60  
  Purchase #7 $99.63   11.378%   $110.9659   $110.97   $110.95   $111.00  
  7 purchase totals = $908.90       $1,013.5036   $1,013.50   $1,013.45   $1,013.60