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 $32.66   6.839%   $34.8936   $34.89   $34.90   $34.90  
  Purchase #2 $218.60   3.683%   $226.651   $226.65   $226.65   $226.70  
  Purchase #3 $48.53   8.832%   $52.8162   $52.82   $52.80   $52.80  
  Purchase #4 $199.96   8.654%   $217.2645   $217.26   $217.25   $217.30  
  Purchase #5 $21.81   11.658%   $24.3526   $24.35   $24.35   $24.40  
  Purchase #6 $38.46   9.282%   $42.0299   $42.03   $42.05   $42.00  
  Purchase #7 $237.30   10.829%   $262.9972   $263.00   $263.00   $263.00  
  7 purchase totals = $797.32       $861.0050   $861.00   $861.00   $861.10