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 $52.87   7.217%   $56.6856   $56.69   $56.70   $56.70  
  Purchase #2 $66.86   13.753%   $76.0553   $76.06   $76.05   $76.10  
  Purchase #3 $21.31   8.287%   $23.076   $23.08   $23.10   $23.10  
  Purchase #4 $115.58   8.873%   $125.8354   $125.84   $125.85   $125.80  
  Purchase #5 $24.46   8.567%   $26.5555   $26.56   $26.55   $26.60  
  Purchase #6 $60.35   12.658%   $67.9891   $67.99   $68.00   $68.00  
  Purchase #7 $7.50   13.624%   $8.5218   $8.52   $8.50   $8.50  
  7 purchase totals = $348.93       $384.7187   $384.74   $384.75   $384.80