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 $57.33   9.213%   $62.6118   $62.61   $62.60   $62.60  
  Purchase #2 $14.96   10.254%   $16.494   $16.49   $16.50   $16.50  
  Purchase #3 $174.59   10.507%   $192.9342   $192.93   $192.95   $192.90  
  Purchase #4 $135.59   8.786%   $147.5029   $147.50   $147.50   $147.50  
  Purchase #5 $67.55   9.208%   $73.77   $73.77   $73.75   $73.80  
  Purchase #6 $234.28   13.254%   $265.3315   $265.33   $265.35   $265.30  
  Purchase #7 $146.78   5.658%   $155.0848   $155.08   $155.10   $155.10  
  7 purchase totals = $831.08       $913.7292   $913.71   $913.75   $913.70