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 $184.95   4.133%   $192.594   $192.59   $192.60   $192.60  
  Purchase #2 $247.66   7.177%   $265.4346   $265.43   $265.45   $265.40  
  Purchase #3 $101.61   9.798%   $111.5657   $111.57   $111.55   $111.60  
  Purchase #4 $207.49   13.681%   $235.8767   $235.88   $235.90   $235.90  
  Purchase #5 $236.68   5.620%   $249.9814   $249.98   $250.00   $250.00  
  Purchase #6 $53.51   8.239%   $57.9187   $57.92   $57.90   $57.90  
  Purchase #7 $126.72   6.285%   $134.6844   $134.68   $134.70   $134.70  
  7 purchase totals = $1,158.62       $1,248.0555   $1,248.05   $1,248.10   $1,248.10