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 $161.49   9.491%   $176.817   $176.82   $176.80   $176.80  
  Purchase #2 $246.73   5.107%   $259.3305   $259.33   $259.35   $259.30  
  Purchase #3 $163.76   5.313%   $172.4606   $172.46   $172.45   $172.50  
  Purchase #4 $98.36   11.149%   $109.3262   $109.33   $109.35   $109.30  
  Purchase #5 $79.98   13.404%   $90.7005   $90.70   $90.70   $90.70  
  Purchase #6 $232.74   6.432%   $247.7098   $247.71   $247.70   $247.70  
  Purchase #7 $93.92   10.796%   $104.0596   $104.06   $104.05   $104.10  
  7 purchase totals = $1,076.98       $1,160.4042   $1,160.41   $1,160.40   $1,160.40