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 $30.49   13.660%   $34.6549   $34.65   $34.65   $34.70  
  Purchase #2 $246.37   9.460%   $269.6766   $269.68   $269.70   $269.70  
  Purchase #3 $21.33   8.131%   $23.0643   $23.06   $23.05   $23.10  
  Purchase #4 $182.67   10.865%   $202.5171   $202.52   $202.50   $202.50  
  Purchase #5 $213.33   10.493%   $235.7147   $235.71   $235.70   $235.70  
  Purchase #6 $56.44   7.690%   $60.7802   $60.78   $60.80   $60.80  
  Purchase #7 $42.63   10.811%   $47.2387   $47.24   $47.25   $47.20  
  7 purchase totals = $793.26       $873.6465   $873.64   $873.65   $873.70