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 $37.41   9.149%   $40.8326   $40.83   $40.85   $40.80  
  Purchase #2 $163.63   3.413%   $169.2147   $169.21   $169.20   $169.20  
  Purchase #3 $202.25   10.160%   $222.7986   $222.80   $222.80   $222.80  
  Purchase #4 $90.51   11.714%   $101.1123   $101.11   $101.10   $101.10  
  Purchase #5 $199.52   3.500%   $206.5032   $206.50   $206.50   $206.50  
  Purchase #6 $73.99   7.777%   $79.7442   $79.74   $79.75   $79.70  
  Purchase #7 $45.34   11.510%   $50.5586   $50.56   $50.55   $50.60  
  7 purchase totals = $812.65       $870.7642   $870.75   $870.75   $870.70