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 $249.88   3.663%   $259.0331   $259.03   $259.05   $259.00  
  Purchase #2 $186.53   12.223%   $209.3296   $209.33   $209.35   $209.30  
  Purchase #3 $61.83   13.184%   $69.9817   $69.98   $70.00   $70.00  
  Purchase #4 $48.43   4.802%   $50.7556   $50.76   $50.75   $50.80  
  Purchase #5 $199.60   13.537%   $226.6199   $226.62   $226.60   $226.60  
  Purchase #6 $51.52   3.258%   $53.1985   $53.20   $53.20   $53.20  
  Purchase #7 $184.47   3.827%   $191.5297   $191.53   $191.55   $191.50  
  7 purchase totals = $982.26       $1,060.4481   $1,060.45   $1,060.50   $1,060.40