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 $55.52   7.348%   $59.5996   $59.60   $59.60   $59.60  
  Purchase #2 $115.76   5.446%   $122.0643   $122.06   $122.05   $122.10  
  Purchase #3 $242.95   8.263%   $263.025   $263.03   $263.05   $263.00  
  Purchase #4 $85.62   3.693%   $88.7819   $88.78   $88.80   $88.80  
  Purchase #5 $181.80   4.177%   $189.3938   $189.39   $189.40   $189.40  
  Purchase #6 $57.36   5.638%   $60.594   $60.59   $60.60   $60.60  
  Purchase #7 $227.39   12.500%   $255.8138   $255.81   $255.80   $255.80  
  7 purchase totals = $966.40       $1,039.2724   $1,039.26   $1,039.30   $1,039.30