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 $63.80   12.659%   $71.8764   $71.88   $71.90   $71.90  
  Purchase #2 $224.59   8.215%   $243.0401   $243.04   $243.05   $243.00  
  Purchase #3 $107.75   9.136%   $117.594   $117.59   $117.60   $117.60  
  Purchase #4 $234.42   11.629%   $261.6807   $261.68   $261.70   $261.70  
  Purchase #5 $16.92   9.350%   $18.502   $18.50   $18.50   $18.50  
  Purchase #6 $137.76   6.867%   $147.22   $147.22   $147.20   $147.20  
  Purchase #7 $174.96   8.622%   $190.0451   $190.05   $190.05   $190.00  
  7 purchase totals = $960.20       $1,049.9583   $1,049.96   $1,050.00   $1,049.90