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 $12.40   10.483%   $13.6999   $13.70   $13.70   $13.70  
  Purchase #2 $50.79   5.377%   $53.521   $53.52   $53.50   $53.50  
  Purchase #3 $139.80   5.705%   $147.7756   $147.78   $147.80   $147.80  
  Purchase #4 $189.46   7.690%   $204.0295   $204.03   $204.05   $204.00  
  Purchase #5 $10.48   6.779%   $11.1904   $11.19   $11.20   $11.20  
  Purchase #6 $46.61   7.427%   $50.0717   $50.07   $50.05   $50.10  
  Purchase #7 $88.69   4.339%   $92.5383   $92.54   $92.55   $92.50  
  7 purchase totals = $538.23       $572.8264   $572.83   $572.85   $572.80