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 $91.69   7.746%   $98.7923   $98.79   $98.80   $98.80  
  Purchase #2 $195.74   9.821%   $214.9636   $214.96   $214.95   $215.00  
  Purchase #3 $59.88   9.293%   $65.4446   $65.44   $65.45   $65.40  
  Purchase #4 $234.67   10.643%   $259.6459   $259.65   $259.65   $259.60  
  Purchase #5 $211.83   10.553%   $234.1844   $234.18   $234.20   $234.20  
  Purchase #6 $184.66   3.107%   $190.3974   $190.40   $190.40   $190.40  
  Purchase #7 $182.89   5.267%   $192.5228   $192.52   $192.50   $192.50  
  7 purchase totals = $1,161.36       $1,255.9510   $1,255.94   $1,255.95   $1,255.90