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 $241.44   8.829%   $262.7567   $262.76   $262.75   $262.80  
  Purchase #2 $139.44   12.576%   $156.976   $156.98   $157.00   $157.00  
  Purchase #3 $58.81   6.345%   $62.5415   $62.54   $62.55   $62.50  
  Purchase #4 $77.37   8.131%   $83.661   $83.66   $83.65   $83.70  
  Purchase #5 $75.37   5.300%   $79.3646   $79.36   $79.35   $79.40  
  Purchase #6 $238.82   4.144%   $248.7167   $248.72   $248.70   $248.70  
  Purchase #7 $29.49   8.309%   $31.9403   $31.94   $31.95   $31.90  
  7 purchase totals = $860.74       $925.9568   $925.96   $925.95   $926.00