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 $167.28   9.543%   $183.2435   $183.24   $183.25   $183.20  
  Purchase #2 $186.75   6.456%   $198.8066   $198.81   $198.80   $198.80  
  Purchase #3 $240.55   5.291%   $253.2775   $253.28   $253.30   $253.30  
  Purchase #4 $152.90   12.870%   $172.5782   $172.58   $172.60   $172.60  
  Purchase #5 $22.79   6.835%   $24.3477   $24.35   $24.35   $24.30  
  Purchase #6 $207.84   9.726%   $228.0545   $228.05   $228.05   $228.10  
  Purchase #7 $188.77   6.296%   $200.655   $200.66   $200.65   $200.70  
  7 purchase totals = $1,166.88       $1,260.9630   $1,260.97   $1,261.00   $1,261.00