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 $210.39   11.567%   $234.7258   $234.73   $234.75   $234.70  
  Purchase #2 $20.67   9.364%   $22.6055   $22.61   $22.60   $22.60  
  Purchase #3 $21.96   4.596%   $22.9693   $22.97   $22.95   $23.00  
  Purchase #4 $64.39   4.535%   $67.3101   $67.31   $67.30   $67.30  
  Purchase #5 $145.37   12.542%   $163.6023   $163.60   $163.60   $163.60  
  Purchase #6 $37.99   10.397%   $41.9398   $41.94   $41.95   $41.90  
  Purchase #7 $34.60   9.643%   $37.9365   $37.94   $37.95   $37.90  
  7 purchase totals = $535.37       $591.0893   $591.10   $591.10   $591.00