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 $243.37   8.870%   $264.9569   $264.96   $264.95   $265.00  
  Purchase #2 $126.43   4.829%   $132.5353   $132.54   $132.55   $132.50  
  Purchase #3 $65.51   4.782%   $68.6427   $68.64   $68.65   $68.60  
  Purchase #4 $143.75   5.792%   $152.076   $152.08   $152.10   $152.10  
  Purchase #5 $115.54   3.150%   $119.1795   $119.18   $119.20   $119.20  
  Purchase #6 $37.99   4.819%   $39.8207   $39.82   $39.80   $39.80  
  Purchase #7 $230.36   13.649%   $261.8018   $261.80   $261.80   $261.80  
  7 purchase totals = $962.95       $1,039.0129   $1,039.02   $1,039.05   $1,039.00