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 $213.99   12.357%   $240.4327   $240.43   $240.45   $240.40  
  Purchase #2 $68.59   9.133%   $74.8543   $74.85   $74.85   $74.90  
  Purchase #3 $236.39   4.242%   $246.4177   $246.42   $246.40   $246.40  
  Purchase #4 $181.52   11.131%   $201.725   $201.73   $201.75   $201.70  
  Purchase #5 $87.34   4.539%   $91.3044   $91.30   $91.30   $91.30  
  Purchase #6 $134.97   12.537%   $151.8912   $151.89   $151.90   $151.90  
  Purchase #7 $11.61   10.135%   $12.7867   $12.79   $12.80   $12.80  
  7 purchase totals = $934.41       $1,019.4120   $1,019.41   $1,019.45   $1,019.40