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 $68.39   7.826%   $73.7422   $73.74   $73.75   $73.70  
  Purchase #2 $60.54   13.178%   $68.518   $68.52   $68.50   $68.50  
  Purchase #3 $70.32   7.485%   $75.5835   $75.58   $75.60   $75.60  
  Purchase #4 $197.66   12.578%   $222.5217   $222.52   $222.50   $222.50  
  Purchase #5 $78.80   10.220%   $86.8534   $86.85   $86.85   $86.90  
  Purchase #6 $242.99   12.788%   $274.0636   $274.06   $274.05   $274.10  
  Purchase #7 $235.51   13.825%   $268.0693   $268.07   $268.05   $268.10  
  7 purchase totals = $954.21       $1,069.3517   $1,069.34   $1,069.30   $1,069.40