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 $176.78   5.441%   $186.3986   $186.40   $186.40   $186.40  
  Purchase #2 $59.26   6.358%   $63.0278   $63.03   $63.05   $63.00  
  Purchase #3 $29.63   10.316%   $32.6866   $32.69   $32.70   $32.70  
  Purchase #4 $207.36   11.171%   $230.5242   $230.52   $230.50   $230.50  
  Purchase #5 $244.71   3.551%   $253.3997   $253.40   $253.40   $253.40  
  Purchase #6 $206.63   8.447%   $224.084   $224.08   $224.10   $224.10  
  Purchase #7 $59.84   6.574%   $63.7739   $63.77   $63.75   $63.80  
  7 purchase totals = $984.21       $1,053.8948   $1,053.89   $1,053.90   $1,053.90