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 $52.25   13.571%   $59.3408   $59.34   $59.35   $59.30  
  Purchase #2 $212.92   7.821%   $229.5725   $229.57   $229.55   $229.60  
  Purchase #3 $235.41   10.637%   $260.4506   $260.45   $260.45   $260.50  
  Purchase #4 $226.79   6.536%   $241.613   $241.61   $241.60   $241.60  
  Purchase #5 $9.77   13.246%   $11.0641   $11.06   $11.05   $11.10  
  Purchase #6 $171.68   12.348%   $192.879   $192.88   $192.90   $192.90  
  Purchase #7 $232.31   11.795%   $259.711   $259.71   $259.70   $259.70  
  7 purchase totals = $1,141.13       $1,254.6310   $1,254.62   $1,254.60   $1,254.70