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 $195.99   10.520%   $216.6081   $216.61   $216.60   $216.60  
  Purchase #2 $17.47   11.738%   $19.5206   $19.52   $19.50   $19.50  
  Purchase #3 $65.88   4.229%   $68.6661   $68.67   $68.65   $68.70  
  Purchase #4 $250.46   10.829%   $277.5823   $277.58   $277.60   $277.60  
  Purchase #5 $217.92   3.434%   $225.4034   $225.40   $225.40   $225.40  
  Purchase #6 $70.73   5.593%   $74.6859   $74.69   $74.70   $74.70  
  Purchase #7 $144.36   10.125%   $158.9765   $158.98   $159.00   $159.00  
  7 purchase totals = $962.81       $1,041.4429   $1,041.45   $1,041.45   $1,041.50