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 $58.94   13.363%   $66.8162   $66.82   $66.80   $66.80  
  Purchase #2 $116.47   12.741%   $131.3094   $131.31   $131.30   $131.30  
  Purchase #3 $200.63   3.512%   $207.6761   $207.68   $207.70   $207.70  
  Purchase #4 $23.64   11.150%   $26.2759   $26.28   $26.30   $26.30  
  Purchase #5 $226.45   3.313%   $233.9523   $233.95   $233.95   $234.00  
  Purchase #6 $124.79   4.443%   $130.3344   $130.33   $130.35   $130.30  
  Purchase #7 $49.64   13.154%   $56.1696   $56.17   $56.15   $56.20  
  7 purchase totals = $800.56       $852.5339   $852.54   $852.55   $852.60