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 $63.40   10.344%   $69.9581   $69.96   $69.95   $70.00  
  Purchase #2 $226.39   5.360%   $238.5245   $238.52   $238.50   $238.50  
  Purchase #3 $37.52   7.544%   $40.3505   $40.35   $40.35   $40.40  
  Purchase #4 $178.42   12.803%   $201.2631   $201.26   $201.25   $201.30  
  Purchase #5 $158.49   8.267%   $171.5924   $171.59   $171.60   $171.60  
  Purchase #6 $161.89   3.477%   $167.5189   $167.52   $167.50   $167.50  
  Purchase #7 $137.87   4.751%   $144.4202   $144.42   $144.40   $144.40  
  7 purchase totals = $963.98       $1,033.6277   $1,033.62   $1,033.55   $1,033.70