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 $229.95   7.706%   $247.6699   $247.67   $247.65   $247.70  
  Purchase #2 $96.45   4.813%   $101.0921   $101.09   $101.10   $101.10  
  Purchase #3 $215.81   8.803%   $234.8078   $234.81   $234.80   $234.80  
  Purchase #4 $171.67   7.565%   $184.6568   $184.66   $184.65   $184.70  
  Purchase #5 $53.70   8.372%   $58.1958   $58.20   $58.20   $58.20  
  Purchase #6 $15.88   9.788%   $17.4343   $17.43   $17.45   $17.40  
  Purchase #7 $211.52   3.863%   $219.691   $219.69   $219.70   $219.70  
  7 purchase totals = $994.98       $1,063.5477   $1,063.55   $1,063.55   $1,063.60