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 $138.83   11.826%   $155.248   $155.25   $155.25   $155.20  
  Purchase #2 $243.59   5.863%   $257.8717   $257.87   $257.85   $257.90  
  Purchase #3 $62.53   7.502%   $67.221   $67.22   $67.20   $67.20  
  Purchase #4 $174.59   13.456%   $198.0828   $198.08   $198.10   $198.10  
  Purchase #5 $131.56   8.293%   $142.4703   $142.47   $142.45   $142.50  
  Purchase #6 $231.62   10.237%   $255.3309   $255.33   $255.35   $255.30  
  Purchase #7 $206.57   5.527%   $217.9871   $217.99   $218.00   $218.00  
  7 purchase totals = $1,189.29       $1,294.2118   $1,294.21   $1,294.20   $1,294.20