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 $71.30   11.623%   $79.5872   $79.59   $79.60   $79.60  
  Purchase #2 $117.98   8.354%   $127.836   $127.84   $127.85   $127.80  
  Purchase #3 $177.67   12.244%   $199.4239   $199.42   $199.40   $199.40  
  Purchase #4 $161.99   12.460%   $182.174   $182.17   $182.15   $182.20  
  Purchase #5 $165.80   13.410%   $188.0338   $188.03   $188.05   $188.00  
  Purchase #6 $205.95   5.873%   $218.0454   $218.05   $218.05   $218.00  
  Purchase #7 $93.26   3.499%   $96.5232   $96.52   $96.50   $96.50  
  7 purchase totals = $993.95       $1,091.6235   $1,091.62   $1,091.60   $1,091.50