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 $225.56   11.174%   $250.7641   $250.76   $250.75   $250.80  
  Purchase #2 $107.36   12.409%   $120.6823   $120.68   $120.70   $120.70  
  Purchase #3 $179.95   10.281%   $198.4507   $198.45   $198.45   $198.50  
  Purchase #4 $171.67   11.153%   $190.8164   $190.82   $190.80   $190.80  
  Purchase #5 $44.54   5.290%   $46.8962   $46.90   $46.90   $46.90  
  Purchase #6 $134.84   6.489%   $143.5898   $143.59   $143.60   $143.60  
  Purchase #7 $170.79   12.130%   $191.5068   $191.51   $191.50   $191.50  
  7 purchase totals = $1,034.71       $1,142.7063   $1,142.71   $1,142.70   $1,142.80