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 $158.95   10.153%   $175.0882   $175.09   $175.10   $175.10  
  Purchase #2 $51.48   6.245%   $54.6949   $54.69   $54.70   $54.70  
  Purchase #3 $168.42   4.270%   $175.6115   $175.61   $175.60   $175.60  
  Purchase #4 $27.93   4.171%   $29.095   $29.10   $29.10   $29.10  
  Purchase #5 $152.94   8.128%   $165.371   $165.37   $165.35   $165.40  
  Purchase #6 $106.82   13.218%   $120.9395   $120.94   $120.95   $120.90  
  Purchase #7 $29.53   10.608%   $32.6625   $32.66   $32.65   $32.70  
  7 purchase totals = $696.07       $753.4626   $753.46   $753.45   $753.50